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Colour temperature is a characteristic of visible light that has important applications in lighting, photography, videography, publishing, manufacturing, astrophysics, and other fields. The color temperature of a light source is the temperature of an ideal black-body radiator that radiates light of comparable hue to that of the light source. Color temperature is conventionally stated in the unit of absolute temperature, the kelvin, having the unit symbol K.
Colour temperatures over 5,000K are called cool colors (blueish white), while lower color temperatures (2,700–3,000 K) are called warm colours (yellowish white through red).
|1,700 K||Match flame|
|1,850 K||Candle flame, sunset/sunrise|
|2,700–3,300 K||Incandescent light bulb|
|3,350 K||Studio "CP" light|
|3,400 K||Studio lamps, photofloods, etc.|
|4,100 K||Moonlight, xenon arc lamp|
|5,000 K||Horizon daylight|
|5,500–6,000 K||Vertical daylight, electronic flash|
|6,500 K||Daylight, overcast|
The colour temperature of the electromagnetic radiation emitted from an ideal black body is defined as its surface temperature in kelvins, or alternatively in mired (micro-reciprocal Kelvin). This permits the definition of a standard by which light sources are compared.
To the extent that a hot surface emits thermal radiation but is not an ideal black-body radiator, the color temperature of the light is not the actual temperature of the surface. An incandescent light bulb's light is thermal radiation and the bulb approximates an ideal black-body radiator, so its color temperature is essentially the temperature of the filament.
Many other light sources, such as fluorescent lamps, emit light primarily by processes other than thermal radiation. This means the emitted radiation does not follow the form of a black-body spectrum. These sources are assigned what is known as a correlated color temperature (CCT). CCT is the color temperature of a black body radiator which to human color perception most closely matches the light from the lamp. Because such an approximation is not required for incandescent light, the CCT for an incandescent light is simply its unadjusted temperature, derived from the comparison to a black body radiator.
For lighting building interiors, it is often important to take into account the colour temperature of illumination. For example, a warmer (i.e., lower colour temperature) light is often used in public areas to promote relaxation, while a cooler (higher color temperature) light is used to enhance concentration in offices.
In fishkeeping, color temperature has different functions and foci, for different branches.
In digital photography, color temperature is sometimes used interchangeably with white balance, which allow a remapping of color values to simulate variations in ambient color temperature. Most digital cameras and RAW image software provide presets simulating specific ambient values (e.g., sunny, cloudy, tungsten, etc.) while others allow explicit entry of white balance values in Kelvin. These settings vary color values along the blue–yellow axis, while some software includes additional controls (sometimes labeled tint) adding the magenta–green axis, and are to some extent arbitrary and subject to artistic interpretation.
Photographic emulsion film sometimes appears to exaggerate the color of the light, since it does not adapt to lighting color as human visual perception does. An object that appears to the eye to be white may turn out to look very blue or orange in a photograph. The colour balance may need to be corrected while shooting or while printing to achieve a neutral color print.
Photographic film is made for specific light sources (most commonly daylight film and tungsten film), and used properly, will create a neutral color print. Matching the sensitivity of the film to the color temperature of the light source is one way to balance color. If tungsten film is used indoors with incandescent lamps, the yellowish-orange light of the tungsten incandescent bulbs will appear as white (3,200 K) in the photograph.
Filters on a camera lens, or colour gels over the light source(s) may also be used to correct color balance. When shooting with a bluish light (high color temperature) source such as on an overcast day, in the shade, in window light or if using tungsten film with white or blue light, a yellowish-orange filter will correct this. For shooting with daylight film (calibrated to 5,600 K) under warmer (low color temperature) light sources such as sunsets, candle light or tungsten lighting, a bluish (e.g., #80A) filter may be used.
If there is more than one light source with varied color temperatures, one way to balance the color is to use daylight film and place color-correcting gel filters over each light source.
Photographers sometimes use color temperature meters. Color temperature meters are usually designed to read only two regions along the visible spectrum (red and blue); more expensive ones read three regions (red, green, and blue). However, they are ineffective with sources such as fluorescent or discharge lamps, whose light varies in color and may be harder to correct for. Because it is often greenish, a magenta filter may correct it. More sophisticated colorimetry tools can be used where such meters are lacking.
In the desktop publishing industry, it is important to know a monitor’s color temperature. Color matching software, such as ColorSync will measure a monitor's color temperature and then adjust its settings accordingly. This enables on-screen color to more closely match printed color. Common monitor color temperatures, along with matching standard illuminants in parentheses, are as follows:
Note: D50 is scientific shorthand for a Standard illuminant: the daylight spectrum at a correlated color temperature of 5,000 K. (Similar definition for D55, D65 and D75.) Designations such as D50 are used to help classify color temperatures of light tables and viewing booths. When viewing a color slide at a light table, it is important that the light be balanced properly so that the colors are not shifted towards the red or blue.
Digital cameras, web graphics, DVDs, etc. are normally designed for a 6,500 K color temperature. The sRGB standard commonly used for images on the internet stipulates (among other things) a 6,500 K display whitepoint.
The NTSC and PAL TV norms call for a compliant TV screen to display an electrically black and white signal (minimal color saturation) at a color temperature of 6,500 K. On many consumer-grade televisions, there is a very noticeable deviation from this requirement. However, higher-end consumer-grade televisions can have their color temperatures adjusted to 6,500 K by using a preprogrammed setting or a custom calibration. Current versions of ATSC explicitly call for the color temperature data to be included in the data stream, but old versions of ATSC allowed this data to be omitted. In this case, current versions of ATSC cite default colorimetry standards depending on the format. Both of the cited standards specify a 6,500 K color temperature.
Most video and digital still cameras can adjust for color temperature by zooming into a white or neutral colored object and setting the manual "white balance" (telling the camera that "this object is white"); the camera then shows true white as white and adjusts all the other colors accordingly. White-balancing is necessary especially when indoors under fluorescent lighting and when moving the camera from one lighting situation to another. Most cameras also have an automatic white balance function that attempts to determine the color of the light and correct accordingly. While these settings were once unreliable, they are much improved in today's digital cameras, and will produce an accurate white balance in a wide variety of lighting situations.
A light-emitting diode (LED is a semiconductor light source. LEDs are used as indicator lamps in many devices and are increasingly used for other lighting. Introduced as a practical electronic component in 1962, early LEDs emitted low-intensity red light, but modern versions are available across the visible, ultraviolet and infrared wavelengths, with very high brightness.
When a light-emitting diode is forward biased (switched on), electrons are able to recombine with electron holes within the device, releasing energy in the form of photons. This effect is called electroluminescence and the colour of the light (corresponding to the energy of the photon) is determined by the energy gap of the semiconductor. An LED is often small in area (less than 1 mm2), and integrated optical components may be used to shape its radiation pattern. LEDs present many advantages over incandescent light sources including lower energy consumption, longer lifetime, improved robustness, smaller size, faster switching, and greater durability and reliability. LEDs powerful enough for room lighting are relatively expensive and require more precise current and heat management than compact fluorescent lamp sources of comparable output.
Light-emitting diodes are used in applications as diverse as replacements for aviation lighting, automotive lighting (particularly brake lamps, turn signals and indicators) as well as in traffic signals. The compact size, the possibility of narrow bandwidth, switching speed, and extreme reliability of LEDs has allowed new text and video displays and sensors to be developed, while their high switching rates are also useful in advanced communications technology. Infrared LEDs are also used in the remote control units of many commercial products including televisions, DVD players, and other domestic appliances.
Efficiency: LEDs emit more light per watt than incandescent light bulbs. Their efficiency is not affected by shape and size, unlike fluorescent light bulbs or tubes.
What Is SMD LED?
SMD LED stands for surface mount LED. Specifically, it's a light-emitting diode that is mounted onto and soldered onto a circuit board. An SMD LED is quite small since it has no leads or surrounding packaging that comes with a standard LED. This means it's best handled, not by a human, but by automated assembly equipment. An SMD LED also has a wide viewing angle, thanks to the fact that it does not have the standard LED's epoxy enclosure that focuses the beam.
Benefits of SMD LED
The SMD LED gives off very little heat. It also has a low voltage and current requirements. Like a standard light emitting diode, a surface mount LED gives off almost no heat. It also typically has similar low voltage and low current requirements. They are commonly used to indicate device status on computer motherboards, routers, hard drives, USB flash drives and any other application where physical space is at a premium. Computer motherboards, hard drives, routers, flash drives and other applications where there's no room for larger technology are also common uses.
Others include LCD display backlighting, keyboard lights, and pushbuttons. They've also been used for instrument panels in aircrafts. A few manufacturers have created an SMD LED lighting solution by combining it with a resistor, small circuit board, lens and cable to provide and bright, cool LED light that runs on just 12 volts, and which is tiny enough to be mounted almost anywhere, (for instance, to light a cup holder).
There are other, large-scale applications, too. For instance, they are used for indoor display screens. SMD LEDs work well because you can arrange a large number of diodes in tight groups of red, blue and green, generating a large variety of colors. This screen technology, which is now found in stores and malls, is now also popping up in large outdoor displays. More information, please come to lighting wiki here.
SMD LED gives high brightness while it has lower power consumption than of a normal LED light tubes (e.g. dip or cluster led) and traditional light bulbs. See its features below:
Small Size: SMD LED light source is a very small and light chips enveloped by epoxy resin.
Low Power Consumption: Generally, the voltage per SMD LED is 2-3.6V, current 0.02A-0.03A. It uses very low voltage and current. Power consumption is very low, just equals to 1/8 of incandescent light, 1/4 of traditional light.
Long Life Span: Under proper current and voltage condition, the life span of SMD LED can reach 100,000 hrs. Compared with the other LED tubes(like Dip LED),the optical decay reduce from 10% to 5% in 1000hrs. Produced by Automatic equipment, via heat emitting technical process, the life span of SMD LED is longer.
High Brightness: Mainly adopted 3528 and 5050 SMD high brightness chip, single SMD LED over 5.5lm/1800MCD.
As above, we have mentioned about SMD 3528 and 5050. What do they mean and what is the difference between the two? Let's see the following:
consists of one light-emitting chip
dimension of chip : 35 x 28 mm
power: 0.08W/ pearl
consists of three light-emitting chips
dimension of chip : 50 x 50 mm
consists of one light-emitting chips
dimension of chip : 56 x 30 mm
Theoretically, SMD5050 is 3 times brighter than SMD3528.But even for the 5050 SMD, there are still many different versions. But there are three are widely used in the lighting industry. 1st:12-14 Lumen each SMD 2nd: 16 -18 lumen each SMD and the 3rd one which is the brightest in the normal applications: 22-24 Lumen each SMD. In LightingXY, our bulbs are normally installed the brightest 5050 chip and for the strips or LED tape, we normally use the 12-14 Lumen SMD unless we have the super bright products. SMD 5630 is high brighter than both 5050 and 3528.
SMD 5050 VS SMD 3528
SMD 3528 Product examples:
SMD 5050 Product examples:
SMD 5630 Samsung Chip Product examples:
You can really see the chips behind the opal lens but one thing I can sure you, it's so powerful!
So much is being said about LED’s in the news and online that consumers are starting to ask, “Why are LED lights better?” LED Lights are better for a number of reasons, one of which is the quality of light, but it doesn’t stop there. In recent years researchers have developed numerous ways in which LED technology could be applied to modern applications. Today, the LED light frenzy is sweeping the nation and it is no surprise! With all of the advantages of using LED lights in comparison to other light forms, there seems to be no contest.
Efficiency: LEDs emit more light per watt than incandescent light bulbs. Their efficiency is not affected by shape and size, unlike fluorescent light bulbs or tubes.
Mosquitoes and bugs are attracted to fluorescent lights and other ultraviolet light sources. Light Emitting Diodes (LED) do not produce ultraviolet light, and therefore mosquitoes are not attracted to them. This makes LED lighting perfect for inside and outside activities.
LED lights do save money, and they do so in a number of different ways. However, some people are reluctant to go out on a limb and spend the additional money to buy them. While it is true that the initial cost of replacing standard lights with LED’s is a bit high, the long term savings will always more than make up for the extra initial expenditure.
The first real benefit of LED light bulbs is that they only use 10% the amount of energy that a regular light bulb uses. Now, if you calculate the total amount of energy that you could save each month by changing all your regular bulbs to LED light bulbs, you will realize that it’s a massive energy saving. And the more energy you save, the more money you save.
The next significant money-saving benefit of LED lights is that they very seldom need any sort of maintenance. The parts that make up an LED light are rugged and durable and a single LED light can last for up to 15 years without needing to be replaced. This means no maintenance which in larger homes and companies converts into monetary savings on maintenance.
After an ordinary light bulb has been on for a few second it becomes too hot to touch do you think an LED light gets too hot in that way why or why not?
LED Lights do not get hot in the sense of creating heat that will burn a person or melt a surface. In fact, an LED bulb that has been on for days can be unscrewed with bare hands! A very small immeasurable amount of heat is generated during the process of the current flowing to the semiconductor, but this heat is so miniscule it can barely be detected. This is one of the greatest advantages of LED lighting for a number of reasons.
Until very recently, many of us weren’t aware of the fact that many ordinary light bulbs contained dangerous heavy metals or poisonous gasses. And if we were aware, it wasn’t made clear just how lethal those substances really are. These same environmentalists are urging consumers to do their part for the delicate ecological balance by using LED lighting throughout the home, office, and even in vehicles and portable devices. It appears as though they feel LED’s are the safest source of artificial light.
A compact fluorescent light is a type of energy-saving bulb that fits into a standard light bulb socket or plugs into a small lighting fixture, and right now, compact fluorescents seem to be gaining in popularity. But did you know they can also be toxic to your home and the environment?
Fluorescent lights are filled with a gas containing low-pressure mercury vapor and argon, or sometimes even krypton. The inner surface of the bulb is coated with a fluorescent coating made of varying blends of metallic and rare earth phosphor salts. Fluorescent light bulbs are more energy efficient than incandescent light bulbs of an equivalent brightness, and the efficiency of fluorescent lighting owes much to low-pressure mercury photon discharges. But fluorescents don't produce a steady light, and they burn out more quickly when cycled frequently; they also contain items such as fluorine, neon, and lead powder as well as mercury.
Alternatives to mercury-containing compact fluorescent lights Fortunately, consumers no longer have to bring mercury into their homes through the use of fluorescent lights. There are now sensible alternatives. One of the most eco-friendly options is LED light bulbs which are not only mercury free, they're also 300% more energy efficient than fluorescent lights (and about 1000% more efficient than incandescent lights).
In photometry, luminous flux or luminous power is the measure of the perceived power of light. It differs from radiant flux, the measure of the total power of light emitted, in that luminous flux is adjusted to reflect the varying sensitivity of the human eye to different wavelengths of light.
The SI unit of luminous flux is the lumen (lm). One lumen is defined as the luminous flux of light produced by a light source that emits one candela of luminous intensity over a solid angle of onesteradian. In other systems of units, luminous flux may have units of power.
The luminous flux accounts for the sensitivity of the eye byweighting the power at each wavelength with the luminosity function, which represents the eye's response to different wavelengths. The luminous flux is a weighted sum of the power at all wavelengths in the visible band. Light outside the visible band does not contribute. The ratio of the total luminous flux to the radiant flux is called theluminous efficacy.
Luminous flux is often used as an objective measure of the useful power emitted by a light source, and is typically reported on the packaging for light bulbs, although it is not always prominent. Energy conscious consumers commonly compare the luminous flux of different light bulbs since it provides an estimate of the apparent amount of light the bulb will produce, and is useful when comparing the luminous efficacy of incandescent and compact fluorescent bulbs.
Luminous flux is not used to compare brightness, as this is a subjective perception which varies according to the distance from the light source.
|Luminous energy||Qv||lumen second||lm·s||units are sometimes calledtalbots|
|Luminous flux||F||lumen (= cd·sr)||lm||also called luminous power|
|Luminous intensity||Iv||candela (= lm/sr)||cd||an SI base unit|
|Luminance||Lv||candela per square metre||cd/m2||units are sometimes called "nits"|
|Illuminance||Ev||lux (= lm/m2)||lx||Used for light incident on a surface|
|Luminous emittance||Mv||lux (= lm/m2)||lx||Used for light emitted from a surface|
|Luminous efficacy||lumen per watt||lm/W||ratio of luminous flux to radiant flux|
A halogen lamp, also known as a tungsten halogen lamp, is an incandescent lamp with atungsten filament contained within an inert gas and a small amount of a halogen such as iodine orbromine. The combination of the halogen gas and the tungsten filament produces a chemical reaction known as a halogen cycle (see below) which increases the lifetime of the filament and prevents darkening of the bulb by redepositing tungsten from the inside of the bulb back onto the filament. Because of this, a halogen lamp can be operated at a higher temperature than a standard gas-filled lamp of similar power and operating life. The higher operating temperature results in light of a higher color temperature. This, in turn, gives it a higher luminous efficacy (10–30 lm/W). Because of their smaller size, halogen lamps can advantageously be used with optical systems that are more efficient in how they cast emitted light.
A fluorescent lamp or fluorescent tube is a gas-discharge lamp that uses electricity to excitemercury vapor. The excited mercury atoms produce short-wave ultraviolet light that then causes aphosphor to fluoresce, producing visible light. A fluorescent lamp converts electrical power into useful light more efficiently than an incandescent lamp. Lower energy cost typically offsets the higher initial cost of the lamp. The lamp fixture is more costly because it requires a ballast to regulate the current through the lamp.
While larger fluorescent lamps have been mostly used in commercial or institutional buildings, thecompact fluorescent lamp is now available in the same popular sizes as incandescents and is used as an energy-saving alternative in homes.
The incandescent light bulb, incandescent lamp or incandescent light globe makes light by heating a metal filament wire to a high temperature until it glows. The hot filament is protected from air by a glass bulb that is filled with inert gas or evacuated. In a halogen lamp, a chemical process that returns metal to the filament prevents its evaporation. The light bulb is supplied with electrical current by feed-through terminals or wires embedded in the glass. Most bulbs are used in a socket (a housing giving mechanical support to the bulb, keeping its terminals in contact with the supply current terminals).
Incandescent bulbs are produced in a wide range of sizes, light output, and voltage ratings, from 1.5 volts to about 300 volts. They require no external regulating equipment and have a low manufacturing cost and work equally well on either alternating current or direct current. As a result, the incandescent lamp is widely used in household and commercial lighting, for portable lighting such as table lamps, car headlamps, and flashlights, and for decorative and advertising lighting.
Some applications of the incandescent bulb use the heat generated by the filament, such as incubators, brooding boxes for poultry, heat lights for reptile tanks, infrared heating for industrial heating and drying processes, and the Easy-Bake Oven toy. In cold weather, the heat produced by incandescent lamps is a benefit as it contributes to building heating, but in hot climates this waste heat increases the energy required by air conditioning systems.
Incandescent light bulbs are gradually being replaced in many applications by other types of electric lights, such as fluorescent lamps, compact fluorescent lamps, cold cathode fluorescent lamps(CCFL), high-intensity discharge lamps, and light-emitting diodes (LEDs). These newer technologies improve the ratio of visible light to heat generation. Some jurisdictions, such as the European Union, are in the process of phasing out the use of incandescent light bulbs in favor of more energy-efficient lighting. In the United States, federal law has scheduled the most common incandescent light bulbs to be phased out by 2014, to be replaced with more energy-efficient light bulbs. In Brazil, they have already been phased out.
Solid-state lighting (SSL) refers to a type of lighting that uses semiconductor light-emitting diodes(LEDs), organic light-emitting diodes (OLED), or polymer light-emitting diodes (PLED) as sources of illumination rather than electrical filaments, plasma (used in arc lamps such as fluorescent lamps), orgas.
The term "solid state" refers commonly to light emitted by solid-state electroluminescence, as opposed to incandescent bulbs (which use thermal radiation) or fluorescent tubes. Compared to incandescent lighting, SSL creates visible light with reduced heat generation or parasitic energy dissipation. Most common "white" LEDs convert blue light from a solid-state device to an (approximate) white light spectrum using photoluminescence, the same principle used in conventional fluorescent tubes.
The typically small mass of a solid-state electronic lighting device provides for greater resistance to shock and vibration compared to brittle glass tubes/bulbs and long, thin filament wires. They also eliminate filament evaporation, potentially increasing the life span of the illumination device.
Solid-state lighting is often used in traffic lights and is also used frequently in modern vehicle lights, street and parking lot lights, train marker lights, building exteriors remote controls etc.
This is a list of sources of light, including both natural and artificial sources, and both processes and devices.
A typical light source emits electromagnetic radiation in the visible spectrum.
Celestial and atmospheric light
A high-intensity discharge (HID) lamp is a type of electrical lamp which produces light by means of an electric arc between tungsten electrodes housed inside a translucent or transparent fused quartz or fused alumina arc tube. This tube is filled with both gas and metal salts. The gas facilitates the arc's initial strike. Once the arc is started, it heats and evaporates the metal salts forming a plasma, which greatly increases the intensity of light produced by the arc and reduces its power consumption. High-intensity discharge lamps are a type of arc lamp.
Compared with fluorescent and incandescent lamps, HID lamps have higher luminous efficacy since a greater proportion of their radiation is in visible light as opposed to heat. Their overall luminous efficacy is also much higher: they give a greater amount of light output per watt of electricity input.
Various different types of chemistry are used in the arc tubes of HID lamps, depending on the desired characteristics of light intensity, correlated color temperature, color rendering index (CRI), energy efficiency, and lifespan. Varieties of HID lamp include:
The light-producing element of these lamp types is a well-stabilized arc discharge contained within a refractory envelope arc tube with wall loading in excess of 3 W/cm² (19.4 W/in²).
Mercury vapor lamps were the first commercially available HID lamps. Originally they produced a bluish-green light, but more recent versions can produce light with a less pronounced color tint. However, mercury vapor lamps are falling out of favor and being replaced by sodium vapor and metal halide lamps.
Metal halide and ceramic metal halide lamps can be made to give off neutral white light useful for applications where normal color appearance is critical, such as TV and movie production, indoor or nighttime sports games, automotive headlamps, and aquarium lighting.
Low-pressure sodium vapor lamps are extremely efficient. They produce a deep yellow-orange light and have an effective CRI of nearly zero; items viewed under their light appear monochromatic. This makes them particularly effective as photographic safe lights. High-pressure sodium lamps tend to produce a much whiter light, but still with a characteristic orange-pink cast. New color-corrected versions producing a whiter light are now available, but some efficiency is sacrificed for the improved color.
Like fluorescent lamps, HID lamps require a ballast to start and maintain their arcs. The method used to initially strike the arc varies: mercury vapor lamps and some metal halide lamps are usually started using a third electrode near one of the main electrodes while other lamp styles are usually started using pulses of high voltage.
HID lamps are typically used when high levels of light over large areas are required, and when energy efficiency and/or light intensity are desired. These areas include gymnasiums, large public areas, warehouses, movie theaters, football stadiums, outdoor activity areas, roadways, parking lots, and pathways. More recently, HID lamps have been used in small retail and residential environments. HID lamps have made indoor gardening practical, particularly for plants that require high levels of direct sunlight in their natural habitat; HID lamps, specifically metal halide and high-pressure sodium, are a common light source for indoor gardens. They are also used to reproduce tropical intensity sunlight for indoor aquaria. Ultra-High Performance (UHP) HID lamps are used in LCD or DLP projection TV sets or projection displays.
Most HID lamps produce significant UV radiation, and require UV-blocking filters to prevent UV-induced degradation of lamp fixture components and fading of dyed items illuminated by the lamp. Exposure to HID lamps operating with faulty or absent UV-blocking filters causes injury to humans and animals, such as sunburn and arc eye. Many HID lamps are designed so as to quickly extinguish if their outer UV-shielding glass envelope is broken.
Beginning in the early 1990s, HID lamps have been employed in motor vehicle headlamps. This application has met with mixed responses from motorists, who appreciate the improved nighttime visibility from HID headlamps but object to the glare they can cause. Internationalized European vehicle regulations require such headlamps to be equipped with lens cleaners and an automatic self-leveling system to keep the beams aimed correctly regardless of vehicle load and altitude, but no such devices are required in North America, where inherently more glaring beam patterns are also permitted. Retrofitting HID bulbs in headlamps not originally designed to accept them results in extremely high levels of glare, and is illegal throughout most of the world.
HID lamps are used in high-performance bicycle headlamps as well as flashlights and other portable lights, because they produce a great amount of light per unit of power. As the HID lights use less than half the power of an equivalent tungsten-halogen light, a significantly smaller and lighter-weight power supply can be used.
HID lamps have also become common on many aircraft as replacements for traditional landing and taxi lights.
HID lamps also become more popular on the high-end dive lights. The mercury-halide lamps have color temperature that well penetrates the water. In addition, HID lamps are more efficient than halogen bulbs, thus permitting longer burn times or smaller batteries. The disadvantage of HID lighting for underwater use is that the bulbs are quite fragile. The other issue is that many HID bulbs require some time (about 25-30 seconds) between re-strikes.
Factors of wear come mostly from on/off cycles versus the total on time. The highest wear occurs when the HID burner is ignited while still hot and before the metallic salts have recrystallized.
At the end of life, many types of high-intensity discharge lamps exhibit a phenomenon known as cycling. These lamps can be started at a relatively low voltage. As they heat up during operation, however, the internal gas pressure within the arc tube rises and a higher voltage is required to maintain the arc discharge. As a lamp gets older, the voltage necessary to maintain the arc eventually rises to exceed the voltage provided by the electrical ballast. As the lamp heats to this point, the arc fails and the lamp goes out. Eventually, with the arc extinguished, the lamp cools down again, the gas pressure in the arc tube is reduced, and the ballast can once again cause the arc to strike. The effect of this is that the lamp glows for a while and then goes out, repeatedly.
More sophisticated ballast designs detect cycling and give up attempting to start the lamp after a few cycles. If power is removed and reapplied, the ballast will make a new series of startup attempts.
Sometimes the quartz tube containing mercury can explode in UHP lamps, especially when it is defective or weakened by many on/off cycles, or when pressure is excessive due to high temperature. When that happens, up to 30 mg vaporized mercury is released into the atmosphere. It can be potentially toxic when indoors. A typical scenario is a failure of UHP HID lamp in front of rear LCD projection TV sets or computer displays. Some vendors recommend use of a mercury vacuum cleaner or respirator when dealing with bulb rupture due to risks of mercury vapors. They also require a special waste disposal.
A light fixture, light fitting, or luminaire is an electrical device used to create artificial light and/or illumination, by use of an electric lamp. All light fixtures have a fixture body, a light socket to hold the lamp and allow for its replacement—which may also have a switch to operate the fixture, and also require an electrical connection to a power source, often by using electrical connectors (e.g. plugs) with portable fixtures. Light fixtures may also have other features, such as reflectors for directing the light, an aperture (with or without a lens), an outer shell or housing for lamp alignment and protection, and an electrical ballast and/or power supply. A wide variety of special light fixtures are created for use in the automotive lighting industry, aerospace, marine and medicine.
The use of the word "lamp" to describe light fixtures is common slang for an all-in-one luminary unit, usually portable "fixtures" such as a table lamp or desk lamp (in contrast to a true fixture, which is fixed in place with screws or some other semi-permanent attachment). In technical terminology, a lamp is the light source, what is typically called the light bulb. (See Lamp (electrical component).)
Light fixtures are classified by how the fixture is installed, the light function or lamp type.
Light fixture is US usage; in British English it is called a light fitting. However, luminaire is the International Electrotechnical Commission (IEC) terminology for technical use.
The lux (symbol: lx) is the SI unit of illuminance and luminous emittance measuring luminous power per area. It is used in photometry as a measure of the intensity, as perceived by the human eye, of light that hits or passes through a surface. It is analogous to the radiometric unit watts per square metre, but with the power at each wavelength weighted according to the luminosity function, a standardized model of human visual brightness perception. In English, "lux" is used in both singular and plural.
Illuminance is a measure of how much luminous flux is spread over a given area. One can think of luminous flux as a measure of the total "amount" of visible light present, and the illuminance is a measure of the intensity of illumination on a surface. A given amount of light will illuminate a surface more dimly if it is spread over a larger area, so illuminance is inversely proportional to area.
In SI, luminous flux is measured in lumens. One lux is equal to one lumen per square metre:
As with other SI units, SI prefixes can be used, for example a kilolux (klx) is 1,000 lux.
|10−4 lux||Total starlight, overcast sky|
|0.002 lux||Moonless clear night sky with airglow|
|0.01 lux||Quarter moon|
|0.27 lux||Full moon on a clear night|
|1 lux||Full moon overhead at tropical latitudes|
|3.4 lux||Dark limit of civil twilight under a clear sky|
|50 lux||Family living room|
|100 lux||Very dark overcast day|
|320–500 lux||Office lighting|
|400 lux||Sunrise or sunset on a clear day.|
|1,000 lux||Overcast day; typical TV studio lighting|
|10,000–25,000 lux||Full daylight (not direct sun)|
|32,000–130,000 lux||Direct sunlight|
Unicode has a symbol for "lx": (㏓). It is a legacy code to accommodate old code pages in some Asian languages. Use of this code is not recommended.
The difference between the lux and the lumen is that the lux takes into account the area over which the luminous flux is spread. A flux of 1,000 lumens, concentrated into an area of one square metre, lights up that square metre with an illuminance of 1,000 lux. However, the same 1,000 lumens, spread out over ten square metres, produces a dimmer illuminance of only 100 lux.
Achieving an illuminance of 500 lux might be possible in a home kitchen with a single fluorescent light fixture with an output of 12,000 lumens. To light a factory floor with dozens of times the area of the kitchen would require dozens of such fixtures. Thus, lighting a larger area to the same level of lux requires a greater number of lumens.
One footcandle ≈ 10.764 lux. The footcandle (or lumen per square foot) is a non-SI unit of illuminance. It is mainly only in common use in the United States, particularly in construction-related engineering and in building codes. Because lux and footcandles are different units of the same quantity, it is perfectly valid to convert footcandles to lux and vice versa.
The name "footcandle" conveys "the illuminance cast on a surface by a one-candela source one foot away." As natural as this sounds, this style of name is now frowned upon, because the dimensional formula for the unit is not foot · candela, but lumen/sq ft. Some sources do however note that the "lux" can be thought of as a "metre-candle" (i.e. the illuminance cast on a surface by a one-candela source one metre away). A source that is farther away provides less illumination than one that is close, so one lux is less illuminance than one footcandle. Since illuminance follows the inverse-square law, and since one foot = 0.3048 m, one lux = 0.30482 footcandle ≈ 1/10.764 footcandle.
In practical applications, as when measuring room illumination, it is very difficult to measure illuminance more accurately than ±10%, and for many purposes it is quite sufficient to think of one footcandle as about ten lux.
Like all photometric units, the lux has a corresponding "radiometric" unit. The difference between any photometric unit and its corresponding radiometric unit is that radiometric units are based on physical power, with all wavelengths being weighted equally, while photometric units take into account the fact that the human eye's visual system is more sensitive to some wavelengths than others, and accordingly every wavelength is given a different weight. The weighting factor is known as the luminosity function.
The lux is one lumen/metre2, and the corresponding radiometric unit, which measures irradiance, is the watt/metre2. There is no single conversion factor between lux and watt/metre2; there is a different conversion factor for every wavelength, and it is not possible to make a conversion unless one knows the spectral composition of the light.
The peak of the luminosity function is at 555 nm (green); the eye's visual system is more sensitive to light of this wavelength than any other. For monochromatic light of this wavelength, the irradiance needed to make one lux is minimum, at 1.464 mW/m2. That is, one obtains 683.002 lux per W/m2 (or lumens per watt) at this wavelength. Other wavelengths of visible light produce fewer lumens per watt. The luminosity function falls to zero for wavelengths outside the visible spectrum.
For a light source with mixed wavelengths, the number of lumens per watt can be calculated by means of the luminosity function. In order to appear reasonably "white," a light source cannot consist solely of the green light to which the eye's visual photoreceptors are most sensitive, but must include a generous mixture of red and blue wavelengths to which they are much less sensitive.
This means that white (or whitish) light sources produce far fewer lumens per watt than the theoretical maximum of 683 lumens per watt. The ratio between the actual number of lumens per watt and the theoretical maximum is expressed as a percentage known as the luminous efficiency. For example, a typical incandescent light bulb has a luminous efficiency of only about 2%.
In reality, individual eyes vary slightly in their luminosity functions. However, photometric units are precisely defined and precisely measurable. They are based on an agreed-upon standard luminosity function which is based on measurements of the spectral characteristics of visual photoreception in many individual human eyes.
Specifications for video cameras such as camcorders and surveillance cameras often include a minimum illuminance level in lux at which the camera will record a satisfactory image. A camera with good low-light capability will have a lower lux rating. Still cameras do not use such a specification, since longer exposure times can generally be used to make pictures at very low illuminance levels, as opposed to the case in video cameras where a maximum exposure time is generally set by the frame rate.
|Luminous energy||Qv||lumen second||lm·s||units are sometimes called talbots|
|Luminous flux||F||lumen (= cd·sr)||lm||also called luminous power|
|Luminous intensity||Iv||candela (= lm/sr)||cd||an SI base unit|
|Luminance||Lv||candela per square metre||cd/m2||units are sometimes called "nits"|
|Illuminance||Ev||lux (= lm/m2)||lx||Used for light incident on a surface|
|Luminous emittance||Mv||lux (= lm/m2)||lx||Used for light emitted from a surface|
|Luminous efficacy||lumen per watt||lm/W||ratio of luminous flux to radiant flux|
|See also SI · Photometry · Radiometry|
The lighting system of a motor vehicle consists of lighting and signalling devices mounted or integrated to the front, sides, rear, and in some cases the top of the vehicle. The purpose of this system is to provide illumination for the driver to operate the vehicle safely after dark, to increase the conspicuity of the vehicle, and to display information about the vehicle's presence, position, size, direction of travel, and driver's intentions regarding direction and speed of travel.
The colour of light emitted by vehicle lights is largely standardised by longstanding convention, first codified in the 1949 Vienna Convention on Road Traffic and later specified in the 1968 United Nations Convention on Road Traffic. Generally, but with some global and regional exceptions, lamps facing rearward must emit red light, lamps facing sideward and all turn signals must emit amber light (though in North America rear turn signals may emit either amber or red light), lamps facing frontward must emit white or selective yellow light, and no other colours are permitted except on emergency vehicles.
Forward illumination is provided by high- ("main", "full", "driving") and low- ("dip", "dipped", "passing") beam headlamps, which may be augmented by auxiliary fog lamps, driving lamps, and/or cornering lamps.
Dipped-beam (also called low, passing, or meeting beam) headlamps provide a light distribution to give adequate forward and lateral illumination without blinding other road users with excessive glare. This beam is specified for use whenever other vehicles are present ahead. The international ECE Regulations for headlamps specify a beam with a sharp, asymmetric cutoff preventing significant amounts of light from being cast into the eyes of drivers of preceding or oncoming cars. Control of glare is less strict in the North American SAE beam standard contained in FMVSS / CMVSS 108.
Main-beam (also called high, driving, or full beam) headlamps provide an intense, centre-weighted distribution of light with no particular control of glare. Therefore, they are only suitable for use when alone on the road, as the glare they produce will dazzle other drivers. International ECE Regulations permit higher-intensity high-beam headlamps than are allowed under North American regulations
"Driving lamp" is a term deriving from the early days of nighttime driving, when it was relatively rare to encounter an opposing vehicle. Only on those occasions when opposing drivers passed each other would the dipped or "passing" beam be used. The full beam was therefore known as the driving beam, and this terminology is still found in international ECE Regulations, which do not distinguish between a vehicle's primary (mandatory) and auxiliary (optional) upper/driving beam lamps. The "driving beam" term has been supplanted in North American regulations by the functionally descriptive term auxiliary high-beam lamp. They are most notably fitted on rallying cars, and are occasionally fitted to production vehicles derived from or imitating such cars. They are common in countries with large stretches of unlit roads, or in regions such as the Nordic countries where the period of daylight is short during winter. Many countries regulate the installation and use of driving lamps. For example, in Russia each vehicle may have no more than three pairs of lights including the original-equipment items, and in Paraguay, auxiliary driving lamps must be off and covered with opaque material when the vehicle is circulating in urban areas.
Vehicles used in rallying, off-roading, or at very high speeds often have extra lamps to broaden and extend the field of illumination in front of the vehicle. On off-road vehicles in particular, these additional lamps are sometimes mounted along with forward-facing lights on a bar above the roof, which protects them from road hazards and raises the beams allowing for a greater projection of light forward.
Front fog lamps provide a wide, bar-shaped beam of light with a sharp cutoff at the top, and are generally aimed and mounted low. They may be either white or selective yellow. They are intended for use at low speed to increase the illumination directed towards the road surface and verges in conditions of poor visibility due to rain, fog, dust or snow. As such, they are often most effectively used in place of dipped-beam headlamps, reducing the glareback from fog or falling snow, although the legality varies by jurisdiction of using front fog lamps without low beam headlamps.
Use of the front fog lamps when visibility is not seriously reduced is often prohibited (for example in the United Kingdom), as they can cause increased glare to other drivers, particularly in wet pavement conditions, as well as harming the driver's own vision due to excessive foreground illumination.
The respective purposes of front fog lamps and driving lamps are often confused, due in part to the misconception that fog lamps are necessarily selective yellow, while any auxiliary lamp that makes white light is a driving lamp. Automakers and aftermarket parts and accessories suppliers frequently refer interchangeably to "fog lamps" and "driving lamps" (or "fog/driving lamps"). In most countries, weather conditions rarely necessitate the use of fog lamps, and there is no legal requirement for them, so their primary purpose is frequently cosmetic. They are often available as optional extras or only on higher trim levels of many cars. Studies have shown that in North America more people inappropriately use their fog lamps in dry weather than use them properly in poor weather.
On some models, white cornering lamps provide extra lateral illumination in the direction of an intended turn or lane change. These are actuated in conjunction with the turn signals, though they burn steadily, and they may also be wired to illuminate when the vehicle is shifted into reverse gear, as is done on many Saabs and Corvettes. North American technical standards contain provisions for front cornering lamps as well as for rear cornering lamps. Cornering lamps have traditionally been prohibited under international ECE Regulations, though provisions have recently been made to allow them as long as they are only operable when the vehicle is travelling at less than 40 kilometres per hour (about 25 mph).
Police cars, emergency vehicles, and those competing in road rallies are sometimes equipped with an auxiliary lamp, sometimes called an alley light, in a swivel-mounted housing attached to one or both a-pillars, directable by a handle protruding through the pillar into the vehicle. Until the mid-1940s, these spot lamps could be found as standard equipment on expensive cars.[which?] Until the mid-1960s, they were commonly offered by automakers as model-specific accessory items. Spot lamps are used to illuminate signs, house numbers, and people. Spot lights can also be had in versions designed to mount through the vehicle's roof. In some countries, for example in Russia, spot lights are allowed only on emergency vehicles or for off-road driving only.
Conspicuity devices are the lamps and reflectors that make a vehicle conspicuous and visible with respect to its presence, position, direction of travel, change in direction or deceleration. Such lamps may burn steadily, blink, or flash, depending on their intended and regulated function.
Nighttime standing-vehicle conspicuity to the front is provided by front position lamps, known as parking lamps or parking lights in North America, and front sidelights in British English. Despite the UK term, these are not the same as the sidemarker lights described below. The front position lamps may emit white or amber light in North America; elsewhere in the world they must emit only white light. Colloquial city light terminology for front position lamps derives from the practice, formerly adhered to in cities like Moscow, London and Paris, of driving at night in built-up areas using these low-intensity lights rather than headlamps. It is now illegal in many countries to drive a vehicle with parking lamps illuminated, unless the headlamps are also illuminated. The UK briefly required Dim-Dip lights, described below, in an attempt to optimise the level of light used at night in built-up areas.
Since the late 1960s, front position lamps have been required to remain illuminated even when the headlamps are on, to maintain the visual signature of a dual-track vehicle to oncoming drivers in the event of headlamp burnout. Front position lamps worldwide produce between 4 and 125 candelas.
In Germany, the StVZO (Road Traffic Licensing Regulations) calls for a different function also known as parking lamps: With the vehicle's ignition switched off, the operator may activate a low-intensity light at the front (white or amber) and rear (red) on either the left or the right side of the car. This function is used when parking in narrow unlit streets to provide parked-vehicle conspicuity to approaching drivers. This function, which is optional under ECE and US regulations, is served passively and without power consumption in North America by the mandatory sidemarker retroreflectors.
Some countries permit or require vehicles to be equipped with daytime running lamps (DRL). These may be functionally-dedicated lamps, or the function may be provided by e.g. the low beam or high beam headlamps, the front turn signals, or the front fog lamps, depending on local regulations. In ECE Regulations, a functionally-dedicated DRL must emit white light with an intensity of at least 400 candelas on axis and no more than 1200 candelas in any direction. Most countries applying ECE Regulations permit low beam headlamps to be used as daytime running lamps. Canada, Sweden, Norway, Slovenia, Finland, Iceland, and Denmark require hardwired automatic DRL systems of varying specification depending on the specific country. DRLs are permitted in many countries where they are not required, but prohibited in other countries not requiring them.
In North America, daytime running lamps may produce up to 7,000 candelas, and can be implemented as high-beam headlamps running at less-than-rated voltage. This has provoked a large number of complaints about glare.
Front, side, and rear position lamps are permitted, required or forbidden to illuminate in combination with daytime running lamps, depending on the jurisdiction and the DRL implementation. Likewise, according to jurisdictional regulations, DRLs mounted within a certain distance of turn signals are permitted or required to extinguish or dim down to parking lamp intensity individually when the adjacent turn signal is operating. A common problem with daytime running lamps is drivers confusing them with automatic headlamps, and failing to turn on their headlamps at dusk. This is extremely dangerous primarily because the driver may not be able to see as clearly because of the dimness associated with daytime running lamps. Also, daytime running lamps fail to illuminate the tail lamps of the vehicle, creating an even more dangerous situation.
U.K. regulations briefly required vehicles first used on or after 1 April 1987 to be equipped with a dim-dip device or special running lamps, except such vehicles as comply fully with ECE Regulation 48 regarding installation of lighting equipment. A dim-dip device operates the low beam headlamps (called "dipped beam" in the UK) at between 10% and 20% of normal low-beam intensity. The running lamps permitted as an alternative to dim-dip were required to emit at least 200 candela straight ahead, and no more than 800 candela in any direction. In practice, most vehicles were equipped with the dim-dip option rather than the running lamps.
The dim-dip systems were not intended for daytime use as DRLs. Rather, they operated if the engine was running and the driver switched on the parking lamps (called "sidelights" in the UK). Dim-dip was intended to provide a nighttime "town beam" with intensity between that of the parking lamps commonly used at the time by British drivers in city traffic after dark, and dipped (low) beams; the former were considered insufficiently intense to provide improved conspicuity in conditions requiring it, while the latter were considered too glaring for safe use in built-up areas. The UK was the only country to require such dim-dip systems, though vehicles so equipped were sold in other Commonwealth countries with left-hand traffic.
In 1988, the European Commission successfully prosecuted the UK government in the European Court of Justice, arguing that the UK requirement for dim-dip was illegal under EC directives prohibiting member states from enacting vehicle lighting requirements not contained in pan-European EC directives. As a result, the UK requirement for dim-dip was quashed. Nevertheless, dim-dip systems remain permitted, and while such systems are not presently as common as they once were, dim-dip functionality was fitted on many new cars well into the 1990s.
In North America, amber front and red rear sidemarker lamps and retro-reflectors are required. The law initially required lights or retroreflectors on vehicles made after 1 January 1968. This was amended to require lights and retroreflectors on vehicles made after 1 January 1970. These side-facing devices make the vehicle's presence, position and direction of travel clearly visible from oblique angles. The lights are wired so as to illuminate whenever the vehicles' parking and taillamps are on, including when the headlamps are being used. Front amber sidemarkers in North America may or may not be wired so as to flash in sync with the turn signals. Sidemarkers are permitted outside North America, but not required. If installed, they are required to be brighter and visible through a larger horizontal angle than US sidemarkers, they may not flash, and they must be amber at the front and rear unless the rear sidemarker is incorporated into the main rear lamp cluster, in which case it may be red or amber. Some Japanese, European, British and US-brand vehicles have sidemarkers in Europe and other countries where they are not required.
Japan's recent accession to internationalised ECE Regulations has caused automakers to change the rear sidemarker colour from red to amber on their models so equipped in the Japanese market.
Turn signals — formally called directional indicators or directional signals, and informally known as "directionals", "blinkers", "indicators" or "flashers" — are signal lights mounted near the left and right front and rear corners of a vehicle, and sometimes on the sides, used to indicate to other drivers that the operator intends a lateral change of position (turn or lane change). Electric turn signal lights were devised as early as 1907. The modern turn signal was patented in 1938 and was later offered by most major automobile manufacturers. Today, turn signals are required on all vehicles that are driven on public roadways in most countries. Alternative systems of hand signals were used earlier, and they are still common for bicycles. Hand signals are also sometimes used when regular vehicle lights are malfunctioning.
Some cars from the 1920s to 1950s used retractable semaphores called trafficators rather than flashing lights. They were commonly mounted high up behind the front doors and swung out horizontally. However, they were fragile and could be easily broken off and also had a tendency to stick in the closed position.
As with all vehicle lighting and signalling devices, turn signal lights must comply with technical standards that stipulate minimum and maximum permissible intensity levels, minimum horizontal and vertical angles of visibility, and minimum illuminated surface area to ensure that they are visible at all relevant angles, do not dazzle those who view them, and are suitably conspicuous in conditions ranging from full darkness to full direct sunlight.
In most countries outside North America, cars must be equipped with side-mounted turn signal repeaters to make the turn indication visible laterally rather than just to the front and rear of the vehicle. These are permitted, but not required in North America. As an alternative in North America, the front amber sidemarker lights may be wired to flash with the turn signals, but this also is not mandatory. In recent years, many automakers have been incorporating side turn signal devices into the sideview mirror housings, rather than mounting them on the vehicle's fenders. One of the first vehicles so equipped was the Mercedes-Benz R170. There is evidence to suggest these mirror-mounted turn signals may be more effective than fender-mounted items.
Turn signals are required to blink on and off, or "flash", at a steady rate of between 60 and 120 blinks per minute (Although some operate slower than this). International regulations require that all turn signals activated at the same time (i.e., all right signals or all left signals) flash in simultaneous phase with one another; North American regulations also require simultaneous operation, but permit sidemarkers wired for side turn signal functionality to flash in opposite-phase. Worldwide regulations stipulate an audiovisual telltale when the turn signals are activated; this usually takes the form of one combined or separate left and right green indicator lights on the vehicle's instrument cluster, and a cyclical "tick-tock" noise generated electromechanically or electronically. It is also required that audio and/or visual warning be provided to the vehicle operator in the event of a turn signal's failure to light. This warning is usually provided by a much faster- or slower-than-normal flash rate, visible on the dashboard indicator, and audible via the faster tick-tock sound.
Turn signals are in almost every case activated by means of a horizontal lever (or "stalk") protruding from the side of the steering column, though some vehicles have the lever mounted instead to the dashboard. The outboard end of the stalk is pushed clockwise to activate the right turn signals, or anticlockwise for the left turn signals. This operation is intuitive; for any given steering manoeuvre, the stalk is pivoted in the same direction as the steering wheel must be turned. In virtually all left-hand drive cars, the signal stalk is on the left side of the column. In right-hand drive cars, the signal stalk may be on either side. If the vehicle's wipers are controlled by a stalk on the opposite side from the signal stalk, a driver unaccustomed to the vehicle may inadvertently activate the wrong control.
Virtually all vehicles (except commercial semi-tractors) have a turn indicator self-cancelling feature that returns the lever to the neutral (no signal) position as the steering wheel approaches the straight-ahead position after a turn has been made. Depending on the configuration of the steering and self-cancelling systems, large-radius turns may not involve enough steering wheel movement to trip the turn signal switch back to the neutral position automatically. However, if the self-cancelling system is configured to avoid this, it may tend to cancel the turn signal prematurely in response to normal steering wheel movement before and during common turns. Beginning in the late 1960s, indicating for a lane change was facilitated by the addition of a spring-loaded momentary signal-on position just shy of the left and right detents. The signal operates for however long the driver holds the lever partway towards the left or right turn signal detent. Some recent vehicles have an automatic lane-change indication feature; tapping the lever partway towards the left or right signal position and immediately releasing it causes the applicable turn indicators to flash three to five times.
Many transit buses, such as those in New York, have, since at least the 1950s, had turn signals activated by floor-mounted momentary-contact footswitches on the floor near the driver's left foot (on left-hand drive buses). The foot-activated signals allow bus drivers to keep both hands on the steering wheel while watching the road and scanning for passengers as they approach a bus stop. New York City Transit bus drivers, among others, are trained to step continuously on the right directional switch while servicing a bus stop, to signal other road users they are intentionally dwelling at the stop, allowing following buses to skip that stop. This method of signalling requires no special arrangements for self-cancellation or passing.
Until the early 1960s, most front turn signals worldwide emitted white light and most rear turn signals emitted red. Amber front turn signals were voluntarily adopted by the auto industry in the USA for most vehicles beginning in the 1963 model year, though front turn signals were still permitted to emit white light until FMVSS 108 took effect for the 1968 model year, whereupon amber became the only permissible colour for front turn signals. Presently, almost all countries outside North America require that all front, side and rear turn signals produce amber light. In North America the rear signals may be amber or red. International proponents of amber rear signals say they are more easily discernible as turn signals. U.S. studies in the early 1990s demonstrated improvements in the speed and accuracy of following drivers' reaction to stop lamps when the turn signals were amber rather than red. American regulators and other proponents of red rear turn signals have historically asserted there is no proven benefit to amber signals. However, a 2008 U.S. study by NHTSA (the National Highway Traffic Safety Administration) suggests vehicles with amber rear signals rather than red ones are up to 28% less likely to be involved in certain kinds of collisions, and a 2009 NHTSA study determined there is a significant overall safety benefit to amber rather than red rear turn signals.
There is some evidence that turn signals with colourless clear lenses and amber bulbs may be less conspicuous in bright sunlight than those with amber lenses and colourless bulbs.
The amber bulbs commonly used in turn signals with colourless lenses are no longer made with cadmium glass, since cadmium was banned because of its toxicity by various regulations worldwide, including the European RoHS directive. Amber glass made without cadmium is relatively costly, so most amber bulbs are now made with clear glass dipped in an amber coating. Some of these coatings are not as durable as the bulbs themselves; with prolonged heat-cool cycles, the coating may flake off the bulb glass, or its colour may fade. This causes the turn signal to emit white light rather than the required amber light. The international regulation on motor vehicle bulbs requires manufacturers to test bulbs for colour endurance. However, no test protocol or colour durability requirement is specified. Discussion is ongoing within the Groupe des Rapporteurs d'Éclairage, the UNECE working group on vehicular lighting regulation, to develop and implement a colour durability standard. Rather than using an amber bulb, some signal lamps contain an inner amber plastic enclosure between a colourless bulb and the colourless outer lens. With the development of high power amber LED lights, it is possible that filament bulbs for turn signals will be made obsolete within a few years.
Sequential turn signals are a feature on some past-model cars whereby multiple lights that produce the rear turn signal do not all flash on and off in phase. Rather, the horizontally-arrayed lamps are illuminated sequentially: the innermost lamp lights and remains illuminated, the next outermost lamp lights and remains illuminated, followed by the next outermost lamp and so on until the outermost lamp lights briefly, at which point all lamps extinguish together and, after a short pause, the cycle begins again. The visual effect is one of outward motion in the direction of the intended turn or lane change. This implementation has generally been found only on American cars that use combination red rear stop and turn signal lamps.
Sequential turn signals were factory fitted to Ford Thunderbirds built between 1965 and 1971, inclusive, to Mercury Cougars between 1967 and 1973, to Shelby Mustangs between 1967 and 1970, to 1969 Imperials (division of Chrysler Corp), to the JDM 1971 Nissan Cedric, and to current Ford Mustangs. The system is costly and complex relative to standard turn signals, and no other production cars were so equipped.
Two different systems were employed. The earlier, fitted to the 1965 through 1968 Ford-built cars, was electro-mechanical, featuring an electric motor driving, through reduction gearing, a set of three slow-turning cams. These cams would actuate switches to turn on the lights in sequence so long as the turn signal switch was set. This system was complicated and prone to failure, and the units no longer function in many surviving cars. Later Ford cars and the 1969 Imperial used a transistorised control module with no moving parts.
FMVSS 108 has been officially interpreted as requiring all turn signal lights to illuminate simultaneously. However, the 2010 Ford Mustang is equipped with sequential turn signals.
Night time vehicle conspicuity to the rear is provided by rear position lamps (also called taillamps or tail lamps, taillights or tail lights). These are required to produce only red light, and to be wired such that they are lit whenever the front position lamps are illuminated—including when the headlamps are on. Rear position lamps may be combined with the vehicle's stop lamps, or separate from them. In combined-function installations, the lamps produce brighter red light for the stop lamp function, and dimmer red light for the rear position lamp function. The tail and stop light functions may be produced separately and/or by a dual-intensity lamp.
Regulations worldwide stipulate minimum intensity ratios between the bright (stop) and dim (tail) modes, so that a vehicle displaying rear position lamps will not be mistakenly interpreted as showing stop lamps, and vice versa.
Many modern designs use LED lighting sources beginning in 1999 with the 2000 Cadillac Deville.
In Europe and other countries adhering to ECE Regulation 48, vehicles must be equipped with one or two bright red "rear fog lamps" (or "fog taillamps"), which serve as high-intensity rear position lamps to be energised by the driver in conditions of poor visibility to enhance vehicle conspicuity from the rear. The allowable range of intensity for a rear fog lamp is 150 to 300 candelas, which is within the range of a U.S. stop lamp. For this reason, some European vehicles imported to the United States have their rear fog lamps wired as stop lamps, since their European-specification stop lamps may not be sufficiently intense to comply with U.S. regulations, and in North America rear fog lamps are not required equipment. However, they are permitted, and are found almost exclusively on European-brand vehicles in North America — Audi, Jaguar, Mercedes, MINI, Land Rover, Porsche, Saab and Volvo provide functional rear fog lights on their North American models. The final generation Oldsmobile Aurora also had dual rear fog lights installed in the rear bumper as standard equipment.
Most jurisdictions permit rear fog lamps to be installed either singly or in pairs. If a single rear fog is fitted, most jurisdictions require it to be located at or to the driver's side of the vehicle's centreline — whichever side is the prevailing driver's side in the country in which the vehicle is registered. This is to maximise the sight line of following drivers to the rear fog lamp. In many cases, a single reversing lamp is mounted on the passenger side of the vehicle, positionally symmetrical with the rear fog. If two rear fog lamps are fitted, they must be symmetrical with respect to the vehicle's centreline. Proponents of twin rear fog lamps say two lamps provide vehicle distance information not available from a single lamp. Proponents of the single rear fog lamp say dual rear fog lamps closely mimic the appearance of illuminated stop lamps (which are mandatorily installed in pairs), reducing the conspicuity of the stop lamps' message when the rear fogs are activated. To provide some safeguard against rear fog lamps being confused with stop lamps, ECE R48 requires a separation of at least 10 cm between the closest illuminated edges of any stop lamp and any rear fog lamp.
Red steady-burning rear lights, brighter than the rear position lamps, are activated when the driver applies the vehicle's brakes. These are called stop lamps, or, colloquially, "brake lights". They are required to be fitted in multiples of two, symmetrically at the left and right edges of the rear of every vehicle. Outside North America, the range of acceptable intensity for a stop lamp containing one light source (e.g. bulb) is 60 to 185 candelas. In North America, the acceptable range for a single-compartment stop lamp is 80 to 300 candelas.
In North America since 1986, in Australia and New Zealand since 1990, and in Europe since 1998, a central brake lamp, mounted higher than the vehicle's left and right brake lamps and called a Centre High Mount Stop Lamp (CHMSL), is also required. The CHMSL (pronounced //) is also sometimes referred to as the centre brake lamp, the third brake light, the eye-level brake lamp, the safety brake lamp, or the high-level brake lamp. The CHMSL may produce light by means of a single central filament bulb, a row or cluster of filament bulbs or LEDs, or a strip of Neon tube.
The CHMSL is intended to provide a deceleration warning to following drivers whose view of the vehicle's left and right stop lamps is blocked by interceding vehicles. It also helps to disambiguate brake vs. turn signal messages in North America, where red rear turn signals identical in appearance to stop lamps are permitted, and also can provide a redundant stop light signal in the event of a stop lamp malfunction.
The CHMSL is generally required to illuminate steadily and not permitted to flash, though U.S. regulators granted Mercedes-Benz a temporary, limited exemption to the steady-light requirement so as to evaluate whether a flashing CHMSL provides an emergency stop signal that effectively reduces the likelihood of a crash.
On passenger cars, the CHMSL may be placed above the back glass, affixed to the vehicle's interior just inside the back glass, or it may be integrated into the vehicle's deck lid or into a spoiler. Other specialised fitments are sometimes seen; the Jeep Wrangler and Land Rover Freelander have the CHMSL on a stalk fixed to the spare wheel carrier. Trucks, vans and commercial vehicles sometimes have the CHMSL mounted to the trailing edge of the vehicle's roof. The CHMSL is required by regulations worldwide to be centred laterally on the vehicle, though ECE R48 permits lateral offset of up to 15 cm if the vehicle's lateral centre is not coincident with a fixed body panel, but instead separates movable components such as doors. The Renault Master van, for example, uses a laterally offset CHMSL for this reason. The height of the CHMSL is also regulated, in absolute terms and with respect to the mounting height of the vehicle's conventional left and right stop lamps. Depending on the left and right lamps' height, the lower edge of the CHMSL may be just above the left and right lamps' upper edge.
The 1968–1971 Ford Thunderbird could be ordered with additional high-mounted stop and turn signal lights. These were fitted in strips on either side of its small rear window. The Oldsmobile Toronado from 1971–1978, and the Buick Riviera from 1974-1976 had dual high-mounted supplemental stop/turn lights as standard, and were located just below the bottom of the backglass, above and ahead of the conventional left and right stop/tail/turn lights. This type of configuration was not widely adopted at the time. Auto and lamp manufacturers in Germany experimented with dual high-mount supplemental stop lamps in the early 1980s, but this effort, too, failed to gain wide popular or regulatory support.
Early studies involving taxicabs and other fleet vehicles found that a third stop lamp reduced rear-end collisions by about 50%. The lamp's novelty probably played a role, since today the lamp is credited with reducing collisions by about 5%.
In 1986, the United States National Highway Traffic Safety Administration and Transport Canada mandated that all new passenger cars have a CHMSL installed. A CHMSL was required on all new light trucks and vans starting in 1994. CHMSLs are so inexpensive to incorporate into a vehicle that even if the lamps prevent only a few percent of rear end collisions they remain a cost-effective safety feature.
Toyota, Mercedes-Benz, Volvo, and BMW have released vehicles equipped to convey a special light signal when the vehicle is braked rapidly and severely. This is officially referred to as Emergency Stop Signal, and ECE Regulation 48 calls for the lamps providing the ESS to flash at 4 Hz when a passenger car decelerates at greater than 6 m/s2 or a truck or bus decelerates at greater than 4 m/s2. Mercedes vehicles flash the stop lamps for the ESS, while vehicles from the Volkswagen Group of manufacturers (VW, Audi, SEAT & Skoda) flash the hazard flashers.
Other methods of severe-braking indication have also been implemented; some Volvo models make the stop lamps brighter, and some BMWs have "Adaptive Brake Lights" that effectively increase the size of the stop lights under severe braking by illuminating the tail lamps at brighter-than-normal intensity. As long as the brighter-than-normal stop lamps are within the regulated maximum intensity for stop lamps in general, this kind of implementation does not require specific regulatory approval since the stop lamps are under all conditions operating in accord with the general regulations on stop lamps.
The idea behind such emergency-braking indicator systems is to catch following drivers' attention with special urgency. However, there remains considerable debate over whether the system offers a measurable increase in safety performance. To date, studies of vehicles in service have not shown any significant such improvement. The systems used by BMW, Volvo, and Mercedes differ not only in operational mode (growing vs. intensifying vs. flashing, respectively), but also in such parameters as deceleration threshold of activation. Data are being collected and analyzed in an effort to determine how such a system might be implemented to maximise a safety benefit, if such a benefit can be realised with visual emergency braking displays. An experimental study at the University of Toronto  has tested stop lights which gradually and continuously grow in illuminated area with increasing vehicle deceleration rate (i.e., increasing brake application pressure).
One potentially problematic factor in the implementation of flashing stop lamps in North America is that North American regulations permit flashing stop lamps to be used in lieu of separate rear turn signal and hazard warning lamps.
To provide illumination to the rear when backing up, and to warn adjacent vehicle operators and pedestrians of a vehicle's rearward motion, each vehicle must be equipped with at least one rear-mounted, rear-facing reversing lamp (or "backup light"). These are currently required to produce white light by U.S. and international ECE regulations. However, some countries have at various times permitted amber reversing lamps. In Australia and New Zealand, for example, vehicle manufacturers were faced with the task of localising American cars originally equipped with combination red stop/turn signal lamps and white reversing lamps. Those countries' regulations permitted the amber rear turn signals to burn steadily as reversing lamps, so automakers and importers were able to combine the (mandatorily amber) rear turn signal and (optionally amber) reversing lamp function, and so comply with the regulations without the need for additional lighting devices. Both countries presently require white reversing lamps, so the combination amber turn/reverse lamp is no longer permitted on new vehicles. The U.S. state of Washington presently permits reversing lamps to emit white or amber light.
The rear registration plate is illuminated by a white lamp designed to light the surface of the plate without creating white light directly visible to the rear of the vehicle; it must be illuminated whenever the position lamps are lit.
Large vehicles such as trucks and buses are in many cases required to carry additional lighting devices beyond those required on passenger vehicles. The specific requirements vary according to the regulations in force where the vehicle is registered and/or operated.
In North America, vehicles over 2,032 mm (80 inches) wide must be equipped with three amber front and three red rear identification lamps spaced between 6 and 12 inches apart at the center of the front and rear of the vehicle, as high as practicable. The front identification lamps are typically mounted atop the cab of vehicles that do not have a flat-nose design. This type of identification lamp can also be found on road trains in Australia.
In North America, vehicles over 2,032 mm (80 inches) wide must be equipped with left and right amber front and red rear clearance lights to indicate the overall width of the vehicle. These must be amber at the front, red at the rear, and mounted as high as practicable.
ECE Regulations require large vehicles to be equipped with left and right white front and red rear end outline marker lamps, which serve a purpose similar to that of the American clearance lamp.
North American regulations require large vehicles to be equipped with left and right amber sidemarker lights and reflectors mounted midway between the front and rear sidemarkers.
Until about the 1970s in France, Spain, Morroco, and possibly other countries, many commercial vehicles and some soviet road trains from "Sovtransavto" had a green light mounted on the rear offside. This could be operated by the driver to indicate that it was safe for the following vehicle to overtake.
Also called "hazards", "hazard warning flashers", "hazard warning lights", "4-way flashers", or simply "flashers". International regulations require vehicles to be equipped with a control which, when activated, flashes the left and right directional signals, front and rear, all at the same time and in phase. This function is meant to be used to indicate a hazard such as a vehicle stopped in or alongside moving traffic, a disabled vehicle, an exceptionally slow-moving vehicle (including, for example, trucks climbing steep grades on Canadian expressways), or the presence of stopped/slow moving traffic ahead on a high speed road. Some people are known to use them in severe fog conditions, or simply when the vehicle has become a traffic hazard. Operation of the hazard flashers must be from a control independent of the turn signal control, and audiovisual telltale must be provided to the driver. In vehicles with a separate left and right green turn signal indicator on the dashboard, both left and right indicators may flash to provide visual indication of the hazard flashers' operation. In some cases, when the driver that has his/her hazard signal ON, and uses the indicator to switch lanes or turn, other road users won't know that the vehicle is switching lanes or turning and therefore causes danger. In vehicles with a single green turn signal indicator on the dashboard, a separate red indicator light must be provided for hazard flasher indication.
A modern vehicle uses different kinds of lamps for multiple purposes: illumination for the driver to be able to drive in dark conditions, illumination to be seen and lights for information displays. Types of these lamps vary depending on the purpose and different car manufacturers and models use different types, with lamp bases adapted for vibration. The types of lamp approved and the bulb designations used vary in different parts of the world.
Beginning in 1958, the United Nations Economic Commission for Europe (UNECE) standardized the following three groups of filament bulb categories to be used in vehicles and trailers sold in Europe. Some ECE-approved bulb types are also permitted by other regulations, such as those of the United States or of Japan—though Japan has adopted ECE regulations.
|R2||2||6V & 12V: 45/40W
|H1||1||6V & 12V: 55W
|ECE, USA, Japan
|H3||1||6V & 12V: 55W
|ECE, USA, Japan
|H4||2||6V & 12V: 60/55W
US designation 9003/HB2
|ECE, USA, Japan
|H8||1||12V: 35W||ECE, USA
PGJ19-1 90° base
|H8B||1||12V: 35W||ECE, USA
PGJY19-1 socketless base
|H9||1||12V: 65W||ECE, USA
PGJ19-5 90° base
|H9B||1||12V: 65W||ECE, USA
PGJY19-5 socketless base
|H10||1||12V: 42W||ECE, USA
PY20d 90° base
PGJ19-2 90° base
PGJY19-2 socketless base
|H12||1||12V: 53W||ECE, USA
PZ20d 90° base
|H13||2||12V: 60/55W||ECE, USA
P26.4t 180° base
|H13A||2||12V: 60/55W||ECE, USA
PJ26.4t 90° base
|H14||2||12V: 60/55W||ECE, Japan
15W filament for DRL function
PGJ23t-1 socketless base
|H21W||1||12V & 24V: 21W||ECE
US designation: 880
PG13 180° base
US designation: 881
PGJ13 90° base
|HB3||1||12V: 60W||ECE, USA
P20d 90° base
|HB3A||1||12V: 60W||ECE, USA
P20d 180° base
|HB4||1||12V: 51W||ECE, USA
P22d 90° base
|HB4A||1||12V: 51W||ECE, USA
P22d 180° base
|HIR1||1||12V: 60W||ECE, USA
PX20d 90° base
|HIR2||1||12V: 55W||ECE, USA
PX22d 90° base
|HS1||2||6V & 12V: 35/35W||ECE
|HS2||1||6V & 12V: 15W||ECE
|S2||2||6V & 12V: 35/35W||ECE
|S3||2||6V & 12V: 15W||ECE
|Category||Cap (Base)||Filaments||Nominal Power|
|C5W||SV8.5||1||6V, 12V, 24V: 5W||Old designation: C11|
|HY21W||BAW9s||1||12V & 24V: 21W||Amber|
|P21W||BA15s||1||6V, 12V, 24V: 21W||Old designation: P25-1|
|PR21W||BAW15s||1||12V & 24V: 21W||Red|
|PY21W||BAU15s||1||12V & 24V: 21W||Amber|
|P21/4W||BAZ15d||2||12V & 24V: 21/4W|
|PR21/4W||BAU15d||2||12V & 24V: 21/4W||Red|
|P21/5W||BAY15d||2||6V, 12V, 24V: 21/5W||Old designation: P25-2|
|PR21/5W||BAW15d||2||12V & 24V: 21/5W||Red|
|P27/7W||W2.5x16q||2||12V: 27/7W||US designation: "3157"|
US variant: "3757A"
|R5W||BA15s||1||6V, 12V, 24V: 5W||Old designation: R19/5|
|RR5W||BAW15s||1||12V & 24V: 5W||Red|
|R10W||BA15s||1||6V, 12V, 24V: 10W||Old designation: R19/10|
|RR10W||BAW15s||1||12V & 24V: 10W||Red|
|RY10W||BAU15s||1||6V, 12V, 24V: 10W||Amber|
|T4W||BA9s||1||6V, 12V, 24V: 4W||Old designation: T8/4|
|W3W||W2.1x9.5d||1||6V, 12V, 24V: 3W||Old designation: W10/3|
|W5W||W2.1x9.5d||1||6V, 12V, 24V: 5W||Old designation: W10/5|
|WR5W||W2.1x9.5d||1||12V & 24V: 5W||Red|
|WY5W||W2.1x9.5d||1||6V, 12V, 24V: 5W||Amber|
|W15/5W||WZ3x16q||2||12V: 15/5W||for motorcycles|
|W16W||W2.1x9.5d||1||12V: 16W||US designation: "921"|
|W21W||W3x16d||1||12V: 21W||US designation: 7440|
US designation: 7440NA
US designation: 7443
|Category||Cap (Base)||Filaments||Nominal power||Comments||Image|
|C21W||SV8.5||1||12V: 21W||Old designation: C15,
for reversing lamp only
|S1||BA20d||2||6V & 12V: 25/25W||for motorcycles|
UNECE has also standardized high-intensity discharge (HID) ("xenon") lamps.
|Category||Cap (Base)||Nominal power||Comments & approvals||Image|
Integral ignitor, for reflector systems
Integral ignitor, for projector systems
For reflector systems
For projector systems
Mercury-free, integral ignitor, for reflector systems
Mercury-free, integral ignitor, for projector systems
Mercury-free, for reflector systems
Mercury-free, for projector systems
The wattage rate of all standardized HID ballasts is 12V/35W.
This section lists lamp types withdrawn from ECE Regulation 37, so are no longer permitted in lamps or vehicles submitted for new type approvals, but which may still be produced for service replacement on older lamps.
Beside the ECE Regulations there are some national regulations in Germany for vehicle bulbs. This regulations are predecessor of the ECE Regulations, but are still in effect. Interchangeable light sources of facilities which have to meet design specifications are required to be conform to an official approved design. That is written in § 22a, Subsection 1, No. 18 of the "Straßenverkehrs-Zulassungs-Ordnung (StVZO)" road traffic admission regulation. As per the "Fahrzeugteileverordnung (FzTV)" vehicle parts regulation from August 12th, 1998, published in the "Bundesgesetzblatt (BGBl.)" federal law publication (BGBl. I S. 2142), lastly changed by Article 6 of the regulation from October 22nd, 2003 (BGBl. I S. 2085), such light bulbs have to have an approval mark, which starts with a sine wave and the letter 'K'. Complementary to the StVZO the "Technische Anforderungen (TA) an Fahrzeugteile as per § 22a StVZO" technological requirements for vehicle parts refers to DIN specifications.
|Category||Nominal power||Filaments||Cap (Base)||Comments||Image|
|Form K (DIN 72601, Part 4)||6V, 10W||1||SV8,5-8||11x41mm|
|Form K (DIN 72601, Part 4)||12V, 10W||1||SV8,5-8||11x41mm|
|Form K (DIN 72601, Part 6)||6V, 18W||1||SV8,5-8||15x41mm|
|Form K (DIN 72601, Part 6)||12V, 18W||1||SV8,5-8||15x41mm|
|Form K (DIN 72601, Part 6)||24V, 18W||1||SV8,5-8||15x41mm|
|Form R (DIN 72601, Part 6)||6V, 18W||1||BA15s|
|Form R (DIN 72601, Part 6)||12V, 18W||1||BA15s|
|Form R (DIN 72601, Part 6)||24V, 18W||1||BA15s|
|Form S (DIN 72601, Part 7)||6V, 18/5W||2||BAY15s|
|Form S (DIN 72601, Part 7)||12V, 18/5W||2||BAY15s|
|Form S (DIN 72601, Part 7)||24V, 18/5W||2||BAY15s|
Internationally-approved bulb designs are not necessarily allowed in the United States, which does not recognize international ECE Regulations. Bulb types allowed for use in headlamps in the United States are individually approved by the National Highway Traffic Safety Administration (NHTSA) after a manufacturer submits all critical data on the bulb required by the provisions of 49CFR564. The allowable types of bulbs (officially known as "replaceable light sources") are filed in a NHTSA Docket.
|Category||Cap (Base)||Filaments||Nominal power @ 12.8v|
European H4 w/strict geometric tolerance & lower max output
|HB3 (9005)||P20d (90°)||1||65W|
|HB3A (9005XS)||P20d (straight)||1||65W||Same as HB3
exc. 180° straight base
|HB4 (9006)||P22d (90°)||1||55W|
|HB4A (9006XS)||P22d (180° straight)||1||55W||Same as HB4
exc. 180° straight base
|H13 (unofficially "9008")||P26t||2||65/55W|
Many types of lamps are used for turn signal, brake lamps, side and clearance marker lamps, and interior lamps. Type numbers standardized by ANSI are used by manufacturers to identify bulbs with the same specifications. Bases may be bayonet-type with one or two contacts, plastic or glass wedge, or other types such as wire-loop or metal caps used on tubular lamps. Screw-base lamps are never used in automobile applications due to their loosening under vibration. Signal lamps may have clear bulbs, or may be coated red or amber to provide extra contrast in brake-lamp and turn-signal applications.
|Category||Cap (Base)||Filaments||Nominal power||Comments||Image|
|PC194||?||1||14V?/3.78W, ?||Used on circuit boards
for e.g. dash lights
|Category||Cap (Base)||Filaments||Electrical Characteristics||Comments||Image|
(USA for unregulated auxiliary lamps only)
They are the same thing. SMD stands for Surface Mount Device. SMT stands for Surface Mount Technology.
LED Headliner composite material
Big sized transparent conductive LED Film
Big sized transparent conductive LED Film
Cuttable LED Strips
The Dictionary of Automotive Terms defines Headliners "as fabric or vinyl upholstery on the interior of the roof of a vehicle". Wikipedias Definition is a bit more informative: "A headliner is a composite material that consists of a face fabric with nonwoven or foam backing that is adhered to the inside roof of automobiles or yachts". This definition reflects the fact, that modern headliner consist of multilayer composite materials which bring together multiple functionalities, i.e. the requested look, haptik, stiffness and soundreduction needed in cars. Also for interior trim component, lighting is a functionality, which is getting more important today. A well known starlight Headliner was produced 2009 for the Rolls-Royce Phantom Sedan. Its starlight consisted of multiple illuminating glass fibers, all connected separately. In other words, the Lighting functionality was not part of the initial composite layers. Automotive companies,, have realized the integration of electroluminescent light panels as dome light behind fabrics. Today, surface mount technology (SMT/SMD) may use 0603 or 0402 SMD LEDs (< 0,3 mm thickness) enabling the production of flexible electronic circuits below 1 mm thickness. As headliner interlayers, they are nealy as thin as electroluminescent panels mentioned above, but they may work with simple 12 VDC without need for electroluminescent inverters. The literature, describes precisely the hot vacuum-lamination of these thin LED Interlayers between glass and polymer composites. A LED Headliner describes a composite Headliner specification containing such an SMD LED Film for lighting purposes.
Purchasers of middleclass automobiles also have preferences for vehicle exteriors with hidden or concealed light sources as a distinguishing decorative appearance for the vehicle. Big efforts are done to provide a lighting arrangement for the interior of an automotive vehicle in which the light source, such as LED, is recessed into the interior structure of the vehicle and covered with a layer of fabric. The light shall shine through the interior trim of the vehicle. Providing invisible light sources when not in use, but enough light through the fabric/foam layer when illuminated, is the main goal of any lighting Headliner.
Since 2006, the Stella Consortium, a group of 12 companies and universities to develop stretchable electronics mounted on fabrics. This solution may open an option for electronics mounted in the last layer of headliners.
LED Headliner consist of multiple layer composite material containing light emitting diode (LED) mounted on electro conductive Films. These films based on printed or transparent conductive Polyester will substitute wires and transport electricity into the roof area of the vehicle, where other overhead systems may be powered. LEDs may be integrated in light guide plate,, if their thickness and their weight will not affect the glueing and laminating process of the headliner. Thermoplastics like Polyester and Polypropylene are already in use in Headliner composites for optimised head impact countermeasure (HIC),. LEDFilm enbedded in LED Headliner may be perforated to enable a well define placement of these films on or to mounting elements within the composite. Perforation may contain Thermoplastic or Adhesive, in different shapes. Example of a shape would be the one of a connecting plug, which is present on both sides of the LED film. This type of connecting plug will reduce vibrations within the LED Film and the LED headliner, which is supposed to absorb noise within its composite. Topview LED will produce small lighting area, starlike, in the Headliner fabric. Sideview LED, with a beam parallel to the substrate surface, will enable bigger area as well as pseudo-homogenious lighting if used in bigger quantities. The best pseudo-homogenious lighting is achieved by embedding side view LED films into transparent polymeric layers, which will act as lightguide materials.
Special interlayers of electroconductive LED Films based on flexible conductive polymers, on flexible printed circuit board or ontransparent conductive metals & oxides sputtered on polymer films which will be laminated between some layers of the composite Headliners.
New automotive composite Headliner base material are disclosed by many different companies,,, allows sound waves originating within a vehicle to penetrate deeply into the headliner where a significant portion of their energy is absorbed rather than reflected back into the vehicle. Consequently, modern headliner composites will often consist of following layers:
9. Release Sheet
8. Scrim Layer
7. Upper porous fibrous layer
6. Upper adhesive layer
5. Closed cell PU - foam
4. Lower porous fibrous layer
3. Lower (sound permeable) adhesive open cell PU barrier
2. Sound permeable cover stock foam layer
1. Coverstock material layer
Internal sound waves within the car will enter the coverstock material layer (1). Sound will diffuse to the upper adhesive layer and it will be reflected by the scrim layer(8). But it will be absorbed all the way through. In the case of LED Headliners one solution would be to laminate the polyester LED Film to the upper adhesive layer (7):
10. Release Sheet
9. Scrim Layer
8. Upper porous fibrous layer
7. Upper adhesive layer
6. Polyester LED Film (full area or perforated)
5. Closed cell PU - foam
4. Lower porous fibrous layer
3. Lower (sound permeable) adhesive open cell PU barrier
2. Sound permeable cover stock foam layer
1. Coverstock material layer
The Polyester LED Film (6) may also be perforated to allow the upper adhesive layer to connect to the closed cell PU foam (5). One possible production process for producing a composite headliner will comprise: Applying adhesive to the different surfaces of the foam cores; placing a fibrous layer to the adhesive coated surface of the foam cores; placing a scrim layer next to the lower porous fiber layers; preparing a coverstock sheet comprising a coverstock material layer and an adhesive barrier; and applying heat (100 - 160 °C) and pressure to the layered materials with a hot press. The pressures and temperatures of the lamination process mentioned above are quite similar to glass laminating temperatures. Consequently not only flexilble printed circuit boards, but also LED embedded films, which are also laminated as inserts at 120 °C to produce transparent LED embedded Glass and dichroic LED Glass are integrated in LED Headliner lamination process.
Surface mount technology (SMT) is a method for constructing electroniccircuits in which the components (SMC, or Surface Mounted Components) are mounted directly onto the surface of printed circuit boards (PCBs). Electronic devices so made are called surface mount devices or SMDs. In the industry it has largely replaced the through-hole technology construction method of fitting components with wire leads into holes in the circuit board.
An SMT component is usually smaller than its through-hole counterpart because it has either smaller leads or no leads at all. It may have short pinsor leads of various styles, flat contacts, a matrix of solder balls (BGAs), or terminations on the body of the component.
Surface mount technology was developed in the 1960s and became widely used in the late 1980s. Much of the pioneering work in this technology was by IBM. The design approach first demonstrated by IBM in 1960 in a small-scale computer was later applied in theLaunch Vehicle Digital Computer used in the Instrument Unit that guided all Saturn IB and Saturn V vehicles. (See Saturn Launch Vehicle Digital Computer article for a description of this type of electronic packaging as of 1964. See  for high-resolution photos of components/PCBs.) Components were mechanically redesigned to have small metal tabs or end caps that could be directly soldered to the surface of the PCB. Components became much smaller and component placement on both sides of a board became far more common with surface mounting than through-hole mounting, allowing much higher circuit densities. Often only the solder joints hold the parts to the board, although parts on the bottom or "second" side of the board are temporarily secured with a dot of adhesive as well. Surface mounted devices (SMDs) are usually made physically small and lightweight for this reason. Surface mounting lends itself well to a high degree of automation, reducing labor cost and greatly increasing production rates. SMDs can be one-quarter to one-tenth the size and weight, and one-half to one-quarter the cost of equivalent through-hole parts.
|SMp DIALECT||Expanded Form|
|SMD||Surface Mount Devices (active, passive and electromechanical components)|
|SMT||Surface Mount Technology (assembling and montage technology)|
|SMA||Surface Mount Assembly (module assembled with SMT)|
|SMC||Surface Mount Components (components for SMT)|
|SMP||Surface Mount Packages (SMD case forms)|
|SME||Surface Mount Equipment (SMT assembling machines)|
|SO||Small Outline (4 to 28 pins)|
|VSO||Very Small Outline (40 pins)|
|SOP||Small Outline Package (case)|
|SOD||Small Outline Diode|
|SOT||Small Outline Transistor|
|SOIC||Small Outline Integrated Circuit|
|LCC||Leadless Chip Carrier|
|PLCC||Plastic Leaded Chip Carrier|
|LCCC||Leadless Ceramic Chip Carrier|
|MELF||Metal Electrode Face Bonding|
|MINI MELF||Mini Metal Electrode Face Bonding|
|MICRO MELF||Micro Metal Electrode Face Bonding|
Where components are to be placed, the printed circuit board has flat, usually tin-lead, silver, or gold plated copper pads without holes, called solder pads. Solder paste, a sticky mixture of flux and tiny solder particles, is first applied to all the solder pads with a stainless steel or nickel stencil using a screen printing process. After screen printing, the boards then proceed to the pick-and-place machines, where they are placed on a conveyor belt. The components to be placed on the boards are usually delivered to the production line in either paper/plastic tapes wound on reels or plastic tubes. Some large integrated circuits are delivered in static-free trays. Numerical control pick-and-place machines remove the parts from the tapes, tubes or trays and place them on the PCB.
The boards are then conveyed into the reflow soldering oven. They first enter a pre-heat zone, where the temperature of the board and all the components is gradually, uniformly raised. The boards then enter a zone where the temperature is high enough to melt the solder particles in the solder paste, bonding the component leads to the pads on the circuit board. The surface tension of the molten solder helps keep the components in place, and if the solder pad geometries are correctly designed, surface tension automatically aligns the components on their pads. There are a number of techniques for reflowing solder. One is to use infrared lamps; this is called infrared reflow. Another is to use a hot gas convection. Another technology which is becoming popular again is special fluorocarbon liquids with high boiling points which use a method calledvapor phase reflow. Due to environmental concerns, this method was falling out of favor until lead-free legislation was introduced which requires tighter controls on soldering. Currently, at the end of 2008, convection soldering is the most popular reflow technology using either standard air or nitrogen gas. Each method has its advantages and disadvantages. With infrared reflow, the board designer must lay the board out so that short components don't fall into the shadows of tall components. Component location is less restricted if the designer knows that vapor phase reflow or convection soldering will be used in production. Following reflow soldering, certain irregular or heat-sensitive components may be installed and soldered by hand, or in large scale automation, by focused infrared beam (FIB) or localized convection equipment.
If the circuit board is double sided then this printing, placement, reflow process may be repeated using either solder paste or glue to hold the components in place. If glue is used then the parts must be soldered later using a wave soldering process.
After soldering, the boards may be washed to remove flux residues and any stray solder balls that could short out closely spaced component leads. Rosin flux is removed with fluorocarbon solvents, high flash point hydrocarbon solvents, or low flash solvents e.g.limonene (derived from orange peels) which require extra rinsing or drying cycles. Water soluble fluxes are removed with deionized waterand detergent, followed by an air blast to quickly remove residual water. However, most electronic assemblies are made using a "No-Clean" process where the flux residues are designed to be left on the circuit board [Benign]. This saves the cost of cleaning, speeds up the whole process, and reduces waste.
Finally, the boards are visually inspected for missing or misaligned components and solder bridging. If needed, they are sent to a rework station where a human operator corrects any errors. They are then sent to the testing stations (in-circuit testing and/or functional testing) to verify that they operate correctly. More information, please come to lighting wiki here.
The main advantages of SMT over the older through-hole technique are:
Defective surface mount components can be repaired in two ways: by using soldering irons (depends on the kind and number of connections) or using a professional rework system. In most cases a rework system is the first choice because the human influence on the rework result is very low. Generally, two essential soldering methods can be distinguished: infrared soldering and soldering with hot gas.
During infrared soldering, the energy for heating up the solder joint will be transmitted by long or short wave electromagnetic radiation.
Conventional hot gas soldering
During hot gas soldering, the energy for heating up the solder joint will be transmitted by a gaseous medium. This can be air or inert gas (nitrogen).
A rework process usually undoes some type of error, either human or machine-generated, and includes the following steps:
Sometimes hundreds or thousands of the same part need to be repaired. Such errors, if due to assembly, are often caught during the process, however a whole new level of rework arises when component failure is discovered too late, and perhaps unnoticed until the end user experiences them. Rework may also be used if high-value products require revisions, and re-engineering, perhaps to change a single firmware based component, may revive a once obsolete product. These tasks require a rework operation specifically designed to repair/replace components in volume.
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Surface mount components are usually smaller than their counterparts with leads, and are designed to be handled by machines rather than by humans. The electronics industry has standardized package shapes and sizes (the leading standardisation body is JEDEC). These include:
There are often subtle variations in package details from manufacturer to manufacturer, and even though standard designations are used, designers need to confirm dimensions when laying out printed circuit boards.
Light pollution, also known as photopollution or luminous pollution, is excessive or obtrusive artificial light.
The International Dark-Sky Association (IDA) defines light pollution as:
Any adverse effect of artificial light including sky glow, glare, light trespass, light clutter, decreased visibility at night, and energy waste.
This approach confuses the cause and its result, however. Pollution is the adding-of/added light itself, in analogy to added sound, carbon dioxide, etc. Adverse consequences are multiple; some of them may be not known yet. Scientific definitions thus include the following:
- Alteration of natural light levels in the outdoor environment owing to artificial light sources.
- Light pollution is the alteration of light levels in the outdoor environment (from those present naturally) due to man-made sources of light. Indoor light pollution is such alteration of light levels in the indoor environment due to sources of light, which compromises human health.
- Light pollution is the introduction by humans, directly or indirectly, of artificial light into the environment.
The first two of the above three scientific definitions describe the state of the environment. The third (and newest) one describes the process of polluting by light.
Light pollution obscures the stars in the night sky for city dwellers, interferes withastronomical observatories, and, like any other form of pollution, disrupts ecosystems and has adverse health effects. Light pollution can be divided into two main types: (1) annoying light that intrudes on an otherwise natural or low-light setting and (2) excessive light (generally indoors) that leads to discomfort and adverse health effects. Since the early 1980s, a globaldark-sky movement has emerged, with concerned people campaigning to reduce the amount of light pollution.
Light pollution is a side effect of industrial civilization. Its sources include building exterior and interior lighting, advertising, commercial properties, offices, factories, streetlights, and illuminated sporting venues. It is most severe in highly industrialized, densely populated areas of North America, Europe, and Japan and in major cities in the Middle East and North Africalike Tehran and Cairo, but even relatively small amounts of light can be noticed and create problems. Like other forms of pollution (such as air, water, and noise pollution) light pollution causes damage to the environment.
Energy conservation advocates contend that light pollution must be addressed by changing the habits of society, so that lighting is used more efficiently, with less waste and less creation of unwanted or unneeded illumination. Several industry groups also recognize light pollution as an important issue. For example, the Institution of Lighting Engineers in the United Kingdom provides its members information about light pollution, the problems it causes, and how to reduce its impact.
Since not everyone is irritated by the same lighting sources, it is common for one person's light "pollution" to be light that is desirable for another. One example of this is found in advertising, when an advertiser wishes for particular lights to be bright and visible, even though others find them annoying. Other types of light pollution are more certain. For instance, light that accidentally crosses a property boundary and annoys a neighbor is generally wasted and pollutive light.
Disputes are still common when deciding appropriate action, and differences in opinion over what light is considered reasonable, and who should be responsible, mean that negotiation must sometimes take place between parties. Where objective measurement is desired, light levels can be quantified by field measurement or mathematical modeling, with results typically displayed as an isophote map or light contour map. Authorities have also taken a variety of measures for dealing with light pollution, depending on the interests, beliefs and understandings of the society involved. Measures range from doing nothing at all, to implementing strict laws and regulations about how lights may be installed and used.
Light pollution is a broad term that refers to multiple problems, all of which are caused by inefficient, unappealing, or (arguably) unnecessary use of artificial light. Specific categories of light pollution include light trespass, over-illumination, glare, light clutter, and skyglow. A single offending light source often falls into more than one of these categories.
Light trespass occurs when unwanted light enters one's property, for instance, by shining over a neighbor's fence. A common light trespass problem occurs when a strong light enters the window of one's home from the outside, causing problems such as sleep deprivation or the blocking of an evening view.
A number of cities in the U.S. have developed standards for outdoor lighting to protect the rights of their citizens against light trespass. To assist them, the International Dark-Sky Association has developed a set of model lighting ordinances. The Dark-Sky Association was started to reduce the light going up into the sky which reduces visibility of stars, see sky glow below. This is any light which is emitted more than 90 degrees above nadir. By limiting light at this 90 degree mark they have also reduced the light output in the 80-90 degree range which creates most of the light trespass issues. U.S. federal agencies may also enforce standards and process complaints within their areas of jurisdiction. For instance, in the case of light trespass by white strobe lighting from communication towers in excess of FAAminimum lighting requirements the Federal Communications Commission maintains an Antenna Structure Registration database information which citizens may use to identify offending structures and provides a mechanism for processing consumer inquiries and complaints. The US Green Building Council (USGBC) has also incorporated into their environmentally friendly building standard known as LEED, a credit for reducing the amount of light trespass and sky glow.
Light trespass can be reduced by selecting light fixtures which limit the amount of light emitted more than 80 degrees above the nadir. The IESNA definitions include full cutoff (0%), cutoff (10%), and semi-cutoff (20%). (These definitions also include limits on light emitted above 90 degrees to reduce sky glow.)
Over-illumination is the excessive use of light. Specifically within the United States, over-illumination is responsible for approximately two million barrels of oil per day in energy wasted. This is based upon U.S. consumption of equivalent of 50 million barrels per day (7,900,000 m3/d) of petroleum. It is further noted in the same U.S. Department of Energy source that over 30 percent of all energy is consumed by commercial, industrial and residential sectors. Energy audits of existing buildings demonstrate that the lighting component of residential, commercial and industrial uses consumes about 20 to 40 percent of those land uses, variable with region and land use. (Residential use lighting consumes only 10 to 30 percent of the energy bill while commercial buildings major use is lighting.) Thus lighting energy accounts for about four or five million barrels of oil (equivalent) per day. Again energy audit data demonstrates that about 30 to 60 percent of energy consumed in lighting is unneeded or gratuitous.
An alternative calculation starts with the fact that commercial building lighting consumes in excess of 81.68 terawatts (1999 data) of electricity, according to the U.S. DOE. Thus commercial lighting alone consumes about four to five million barrels per day (equivalent) of petroleum, in line with the alternate rationale above to estimate U.S. lighting energy consumption.
Over-illumination stems from several factors:
Most of these issues can be readily corrected with available, inexpensive technology, and with resolution of landlord/tenant practices that create barriers to rapid correction of these matters. Most importantly public awareness would need to improve for industrialized countries to realize the large payoff in reducing over-illumination.
Glare can be categorized into different types. One such classification is described in a book by Bob Mizon, coordinator for the British Astronomical Association's Campaign for Dark Skies. According to this classification:
According to Mario Motta, president of the Massachusetts Medical Society, "... glare from bad lighting is a public-health hazard—especially the older you become. Glare light scattering in the eye causes loss of contrast and leads to unsafe driving conditions, much like the glare on a dirty windshield from low-angle sunlight or the high beams from an oncoming car." In essence bright and/or badly shielded lights around roads can partially blind drivers or pedestrians and contribute to accidents.
The blinding effect is caused in large part by reduced contrast due to light scattering in the eye by excessive brightness, or to reflection of light from dark areas in the field of vision, with luminance similar to the background luminance. This kind of glare is a particular instance of disability glare, called veiling glare. (This is not the same as loss of accommodation of night vision which is caused by the direct effect of the light itself on the eye.)
Light clutter refers to excessive groupings of lights. Groupings of lights may generate confusion, distract from obstacles (including those that they may be intended to illuminate), and potentially cause accidents. Clutter is particularly noticeable on roads where the street lights are badly designed, or where brightly lit advertising surrounds the roadways. Depending on the motives of the person or organization that installed the lights, their placement and design can even be intended to distract drivers, and can contribute to accidents.
Clutter may also present a hazard in the aviation environment if aviation safety lighting must compete for pilot attention with non-relevant lighting. For instance, runway lighting may be confused with an array of suburban commercial lighting and aircraft collision avoidance lights may be confused with ground lights.
Skyglow refers to the "glow" effect that can be seen over populated areas. It is the combination of all light reflected from what it has illuminated escaping up into the sky and from all of the badly directed light in that area that also escapes into the sky, being scattered (redirected) by the atmosphere back toward the ground. This scattering is very strongly related to the wavelength of the light when the air is very clear (with very little aerosols).Rayleigh scattering dominates in such clear air, making the sky appear blue in the daytime. When there is significant aerosol (typical of most modern polluted conditions), the scattered light has less dependence on wavelength, making a whiter daytime sky. Because of this Rayleigh effect, and because of the eye's increased sensitivity to white or blue-rich light sources when adapted to very low light levels (see Purkinje effect), white or blue-rich light contributes significantly more to sky-glow than an equal amount of yellow light. Sky glow is of particular irritation to astronomers, because it reduces contrast in the night sky to the extent where it may even become impossible to see any but the brightest stars.
The Bortle Dark-Sky Scale, originally published in Sky & Telescope magazine, is sometimes used (by groups like the U.S.National Park Service) to quantify skyglow and general sky clarity. The nine-class scale rates the darkness of the night sky and the visibility of its phenomena, such as the gegenschein and the zodiacal light (easily masked by skyglow), providing a detailed description of each level on the scale (with Class 1 being the best).
Light is particularly problematic for amateur astronomers, whose ability to observe the night sky from their property is likely to be inhibited by any stray light from nearby. Most major optical astronomical observatories are surrounded by zones of strictly enforced restrictions on light emissions.
"Direct" skyglow is reduced by selecting lighting fixtures which limit the amount of light emitted more than 90 degrees above the nadir. The IESNA definitions include full cutoff (0%), cutoff (2.5%), and semi-cutoff (5%). "Indirect" skyglow produced by reflections from vertical and horizontal surfaces is harder to manage; the only effective method for preventing it is by minimizing over-illumination. But it has to be taken into account that according to late 2010 publications reported by Monthly Notices of Royal Astronomical Society ("Campaign of sky brightness and extinction measurements by using a portable CCD Camera", F. Falchi) Italian regions using full cut off lighting only does not increase skyglow. Anyway light reflected upwards by dark surfaces such as roads or building can be considered as minor, so debate about contribution of "indirect" skyglow will last long.
Skyglow is made considerably worse when clouds are present. While this has no effect on astronomical observations (which are not possible at visible wavelengths under cloud cover), it is very important in the context of ecological light pollution. Since cloudy nights can be up to ten times brighter than clear nights, any organisms that are affected by sky glow (e.g. zooplankton and fish that visually prey on them) are much more likely to have their ordinary behavior disturbed on cloudy nights.
Measuring the effect of sky glow on a global scale is a complex procedure. The natural atmosphere is not completely dark, even in the absence of terrestrial sources of light and illumination from the Moon. This is caused by two main sources: airglow and scattered light.
At high altitudes, primarily above the mesosphere, there is enough UV radiation from the sun of very short wavelength that ionization occurs. When these ions collide with electrically neutral particles they recombine and emit photons in the process, causing airglow. The degree of ionization is sufficiently large to allow a constant emission of radiation even during the night when the upper atmosphere is in the Earth's shadow. Lower in the atmosphere all of the solar photons with energies above the ionization potential of N2 and O2 have already been absorbed by the higher layers and thus no appreciable ionization occurs.
Apart from emitting light, the sky also scatters incoming light, primarily from distant stars and the Milky Way, but also the zodiacal light, sunlight that is reflected and backscattered from interplanetary dust particles.
The amount of airglow and zodiacal light is quite variable (depending, amongst other things on sunspot activity and the Solar cycle) but given optimal conditions the darkest possible sky has a brightness of about 22 magnitude/square arcsecond. If a full moon is present, the sky brightness increases to 18 magnitude/sq. arcsecond, 40 times brighter than the darkest sky. In densely populated areas a sky brightness of 17 magnitude/sq. arcsecond is not uncommon, or as much as 100 times brighter than is natural.
To precisely measure how bright the sky gets, night time satellite imagery of the earth is used as raw input for the number and intensity of light sources. These are put into a physical model of scattering due to air molecules and aerosoles to calculate cumulative sky brightness. Maps that show the enhanced sky brightness have been prepared for the entire world.
Inspection of the area surrounding Madrid reveals that the effects of light pollution caused by a single large conglomeration can be felt up to 100 km (62 mi) away from the center. Global effects of light pollution are also made obvious. The entire area consisting of southern England, Netherlands, Belgium, west Germany, and northern France have a sky brightness of at least 2 to 4 times above normal (see above right). The only places in continental Europe where the sky can attain its natural darkness is in northern Scandinavia and in islands far from the continent.
In North America the situation is comparable. From the east coast to west Texas up to the Canadian border there is very significant global light pollution.
Lighting is responsible for one-fourth of all electricity consumption worldwide, and case studies have shown that several forms of over-illumination constitute energy wastage, including non-beneficial upward direction of night-time lighting. In 2007, Terna, the company responsible for managing electricity flow in Italy, reported a saving of 645.2 million kWh in electricity consumption during the daylight saving period from April to October. It attributes this saving to the delayed need for artificial lighting during the evenings.
... public lighting is the single largest source of local government's greenhouse gas emissions, typically accounting for 30 to 50% of their emissions. There are 1.94 million public lights — one for every 10 Australians — that annually cost A$210 million, use 1,035 GWh of electricity and are responsible for 1.15 million tonnes of CO2 emissions.
Current public lighting in Australia, particularly for minor roads and streets, uses large amounts of energy and financial resources, while often failing to provide high quality lighting. There are many ways to improve lighting quality while reducing energy use and greenhouse gas emissions as well as lowering costs.
Medical research on the effects of excessive light on the human body suggests that a variety of adverse health effects may be caused by light pollution or excessive light exposure, and some lighting design textbooks use human health as an explicit criterion for proper interior lighting. Health effects of over-illumination or improper spectral composition of light may include: increased headache incidence, worker fatigue, medically defined stress, decrease insexual function and increase in anxiety. Likewise, animal models have been studied demonstrating unavoidable light to produce adverse effect on mood and anxiety.For those who need to be awake at night, light at night also has an acute effect on alertness and mood.
Common levels of fluorescent lighting in offices are sufficient to elevate blood pressure by about eight points. Specifically within the USA, there is evidence that levels of light in most office environments lead to increased stress as well as increased worker errors.
Several published studies also suggest a link between exposure to light at night and risk of breast cancer, due to suppression of the normal nocturnal production of melatonin. In 1978 Cohen et al. proposed that reduced production of the hormone melatonin might increase the risk of breast cancer and citing "environmental lighting" as a possible causal factor. Researchers at the National Cancer Institute (NCI) and National Institute of Environmental Health Sciences have also concluded a study that suggests that artificial light during the night can be a factor for breast cancer.
In 2007, "shift work that involves circadian disruption" was listed as a probable carcinogen by the World Health Organization's International Agency for Research on Cancer. (IARC Press release No. 180). Multiple studies have documented a correlation between night shift work and the increased incidence of breast cancer.
A good review of current knowledge of the health consequences of exposure to artificial light at night and an explanation of the causal mechanisms has been published in the Journal of Pineal Research in 2007.
A more recent discussion (2009), written by Professor Steven Lockley, Harvard Medical School, can be found in the CfDS handbook "Blinded by the Light?". Chapter 4, "Human health implications of light pollution" states that "... light intrusion, even if dim, is likely to have measurable effects on sleep disruption and melatonin suppression. Even if these effects are relatively small from night to night, continuous chronic circadian, sleep and hormonal disruption may have longer-term health risks". The New York Academy of Sciences hosted a meeting in 2009 on Circadian Disruption and Cancer. Forty Danish female shift workers in 2009 were awarded compensation for breast cancer "caused" by shift work made possible by light at night - the most common cause of light pollution.
In June 2009, the American Medical Association developed a policy in support of control of light pollution. News about the decision emphasized glare as a public health hazard leading to unsafe driving conditions. Especially in the elderly, glare produces loss of contrast, obscuring night vision.
Light pollution poses a serious threat to wildlife, having negative impacts on plant and animal physiology. Light pollution can confuse animal navigation, alter competitive interactions, change predator-prey relations, and cause physiological harm. The rhythm of life is orchestrated by the natural diurnal patterns of light and dark, so disruption to these patterns impacts the ecological dynamics.
Studies suggest that light pollution around lakes prevents zooplankton, such as Daphnia, from eating surface algae, helping cause algal blooms that can kill off the lakes' plants and lower water quality. Light pollution may also affect ecosystems in other ways. For example, lepidopterists and entomologists have documented that nighttime light may interfere with the ability of moths and other nocturnal insects to navigate. Night-blooming flowers that depend on moths for pollination may be affected by night lighting, as there is no replacement pollinator that would not be affected by the artificial light. This can lead to species decline of plants that are unable to reproduce, and change an area's longterm ecology.
A 2009 study also suggests deleterious impacts on animals and ecosystems because of perturbation of polarized light or artificial polarisation of light (even during the day, because direction of natural polarization of sun light and its reflexion is a source of information for a lot of animals). This form of pollution is named polarized light pollution (PLP). Unnatural polarized light sources can trigger maladaptive behaviors in polarization-sensitive taxa and alter ecological interactions.
Lights on tall structures can disorient migrating birds. Estimates by the U.S. Fish and Wildlife Service of the number of birds killed after being attracted to tall towers range from 4 to 5 million per year to an order of magnitude higher. The Fatal Light Awareness Program (FLAP) works with building owners in Toronto, Canada and other cities to reduce mortality of birds by turning out lights during migration periods.
Similar disorientation has also been noted for bird species migrating close to offshore production and drilling facilities. Studies carried out by Nederlandse Aardolie Maatschappij b.v. (NAM) and Shell have led to development and trial of new lighting technologies in the North Sea. In early 2007, the lights were installed on the Shell production platform L15. The experiment proved a great success since the number of birds circling the platform declined by 50 to 90%.
Sea turtle hatchlings emerging from nests on beaches are another casualty of light pollution. It is a common misconception that hatchling sea turtles are attracted to the moon. Rather, they find the ocean by moving away from the dark silhouette of dunes and their vegetation, a behavior with which artificial lights interfere. The breeding activity and reproductive phenology of toads, however, are cued by moonlight. Juvenile seabirds may also be disoriented by lights as they leave their nests and fly out to sea. Amphibians and reptiles are also affected by light pollution. Introduced light sources during normally dark periods can disrupt levels of melatonin production. Melatonin is a hormone that regulates photoperiodic physiology and behaviour. Some species of frogs and salamanders utilize a light-dependent "compass" to orient their migratory behaviour to breeding sites. Introduced light can also cause developmental irregularities, such as retinal damage, reduced sperm production, and genetic mutation.
In September 2009, the 9th European Dark-Sky Symposium in Armagh, Northern Ireland had a session on the environmental effects of light at night (LAN). It dealt with bats, turtles, the "hidden" harms of LAN, and many other topics. The environmental effects of LAN were mentioned as early as 1897, in a Los Angeles Times article—the text of which can be obtained from Dr. Travis Longcore of the Urban Wildlands Trust, California. The following is an excerpt from that article, called "Electricity and English songbirds":
An English journal has become alarmed at the relation of electricity to songbirds, which it maintains is closer than that of cats and fodder crops. How many of us, it asks, foresee that electricity may extirpate the songbird?...With the exception of the finches, all the English songbirds may be said to be insectivorous, and their diet consists chiefly of vast numbers of very small insects which they collect from the grass and herbs before the dew is dry. As the electric light is finding its way for street illumination into the country parts of England, these poor winged atoms are slain by thousands at each light every warm summer evening....The fear is expressed, that when England is lighted from one end to the other with electricity the song birds will die out from the failure of their food supply.
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Astronomy, both amateur and professional, is very sensitive to light pollution. The night sky viewed from a city bears no resemblance to what can be seen from dark skies. Skyglow (the scattering of light in the atmosphere) reduces the contrast between stars and galaxies and the sky itself, making it very much harder see fainter objects. This is one factor that has caused newer telescopes to be built in increasingly remote areas. Some astronomers use narrow-band "nebula filters" which only allow specific wavelengths of light commonly seen in nebulae, or broad-band "light pollution filters" which are designed to reduce (but not eliminate) the effects of light pollution by filtering out spectral lines commonly emitted by sodium- andmercury-vapor lamps, thus enhancing contrast and improving the view of dim objects such asgalaxies and nebulae. Unfortunately these light pollution reduction (LPR) filters are not a cure for light pollution. LPR filters reduce the brightness of the object under study and this limits the use of higher magnifications. LPR filters work by blocking light of certain wavelengths, which alters the color of the object, often creating a pronounced green cast. Furthermore, LPR filters only work on certain object types (mainly emission nebulae) and are of little use on galaxies and stars. No filter can match the effectiveness of a dark sky for visual or photographic purposes. Due to their low surface brightness, the visibility of diffuse sky objects such as nebulae and galaxies is affected by light pollution more than are stars. Most such objects are rendered invisible in heavily light polluted skies around major cities. A simple method for estimating the darkness of a location is to look for the Milky Way, which from truly dark skies appears bright enough to cast a shadow.
In addition to skyglow, light trespass can impact observations when artificial light directly enters the tube of the telescope and is reflected from non-optical surfaces until it eventually reaches the eyepiece. This direct form of light pollution causes a glow across thefield of view which reduces contrast. Light trespass also makes it hard for a visual observer to become sufficiently dark adapted. The usual measures to reduce this glare, if reducing the light directly is not an option, include flocking the telescope tube and accessories to reduce reflection, and putting a light shield (also usable as a dew shield) on the telescope to reduce light entering from angles other than those near the target. Under these conditions, some astronomers prefer to observe under a black cloth to ensure maximum dark adaptation. In one Italian regional lighting code this effect of stray light is defined as "optical pollution", due to the fact that there is a direct path from the light source to the "optic" - the observer's eye or telescope.
A study presented at the American Geophysical Union meeting in San Francisco found that light pollution destroys nitrate radicals thus preventing the normal night time reduction of atmospheric smog produced by fumes emitted from cars and factories. The study was presented by Harald Stark from the National Oceanic and Atmospheric Administration.
Reducing light pollution implies many things, such as reducing sky glow, reducing glare, reducing light trespass, and reducing clutter. The method for best reducing light pollution, therefore, depends on exactly what the problem is in any given instance. Possible solutions include:
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The use of full cutoff lighting fixtures, as much as possible, is advocated by most campaigners for the reduction of light pollution. It is also commonly recommended that lights be spaced appropriately for maximum efficiency, and that lamps within the fixtures not be overpowered.
Full cutoff fixtures first became available in 1959 with the introduction of General Electric's M100 fixture.
A full cutoff fixture, when correctly installed, reduces the chance for light to escape above the plane of the horizontal. Light released above the horizontal may sometimes be lighting an intended target, but often serves no purpose. When it enters into the atmosphere, light contributes to sky glow. Some governments and organizations are now considering, or have already implemented, full cutoff fixtures in street lamps and stadium lighting.
The use of full cutoff fixtures help to reduce sky glow by preventing light from escaping above the horizontal. Full cutoff typically reduces the visibility of the lamp and reflector within a luminaire, so the effects of glare are also reduced. Campaigners also commonly argue that full cutoff fixtures are more efficient than other fixtures, since light that would otherwise have escaped into the atmosphere may instead be directed towards the ground. However, full cutoff fixtures may also trap more light in the fixture than other types of luminaires, corresponding to lower luminaire efficiency, suggesting a re-design of some luminaires may be necessary.
The use of full cutoff fixtures can allow for lower wattage lamps to be used in the fixtures, producing the same or sometimes a better effect, due to being more carefully controlled. In every lighting system, some sky glow also results from light reflected from the ground. This reflection can be reduced, however, by being careful to use only the lowest wattage necessary for the lamp, and setting spacing between lights appropriately. Assuring luminaire setback is greater than 90 degrees from highly reflective surfaces also diminishes reflectance.
A common criticism of full cutoff lighting fixtures is that they are sometimes not as aesthetically pleasing to look at. This is most likely because historically there has not been a large market specifically for full cutoff fixtures, and because people typically like to see the source of illumination. Due to the specificity with their direction of light, full cutoff fixtures sometimes also require expertise to install for maximum effect.
The effectiveness of using full cutoff roadway lights to combat light pollution has also been called into question. According to design investigations, luminaires with full cutoff distributions (as opposed to cutoff or semi cutoff, compared here ) have to be closer together to meet the same light level, uniformity and glare requirements specified by the IESNA. These simulations optimized the height and spacing of the lights while constraining the overall design to meet the IESNA requirements, and then compared total uplight and energy consumption of different luminaire designs and powers. Cutoff designs performed better than full cutoff designs, and semi-cutoff performed better than either cutoff or full cutoff. This indicates that, in roadway installations, over-illumination or poor uniformity produced by full cutoff fixtures may be more detrimental than direct uplight created by fewer cutoff or semi-cutoff fixtures. Therefore, the overall performance of existing systems could be improved more by reducing the number of luminaires than by switching to full cutoff designs.
However, using the definition of "light pollution" from some Italian regional bills (i.e., "every irradiance of artificial light outside competence areas and particularly upward the sky") only full cutoff design prevents light pollution. The Italian Lombardy region, where only full cutoff design is allowed (Lombardy act no. 17/2000, promoted by Cielobuio-coordination for the protection of the night sky), in 2007 had the lowest per capita energy consumption for public lighting in Italy: this information can be verified using data released by Terna company. The same legislation also imposes a minimum distance between street lamps of about four times their height, so full cut off street lamps are the best solution to reduce both light pollution and electrical power usage.
Several different types of light sources exist, each having different properties that affect their appropriateness for certain tasks, particularly efficiency and spectral power distribution. It is often the case that inappropriate light sources have been selected for a task, either due to ignorance or because more sophisticated light sources were unavailable at the time of installation. Therefore, badly chosen light sources often contribute unnecessarily to light pollution and energy waste. By re-assessing and changing the light sources used, it is often possible to reduce energy use and pollutive effects while simultaneously greatly improving efficiency and visibility.
Some types of light sources are listed in order of energy efficiency in the table below.
|Type of light source||Color||Luminous effectiveness|
(in lumens per watt)
|Low Pressure Sodium (LPS/SOX)||yellow/amber||80–200|
|High Pressure Sodium(HPS/SON)||pink/amber-white||90–130|
Many astronomers request that nearby communities use low pressure sodium lights as much as possible, because the principal wavelength emitted is comparably easy to work around or in rare cases filter out. The low cost of operating sodium lights is another feature. In 1980, for example, San Jose, California, replaced all street lamps with low pressure sodium lamps, whose light is easier for nearby Lick Observatory to filter out. Similar programs are now in place in Arizona and Hawaii.
Disadvantages of low pressure sodium lighting are that fixtures must usually be larger than competing fixtures, and that color cannot be distinguished, due to its emitting principally a single wavelength of light (see security lighting). Due to the substantial size of the lamp, particularly in higher wattages such as 135 W and 180 W, control of light emissions from low pressure sodium luminaires is more difficult. For applications requiring more precise direction of light (such as narrow roadways) the native lamp efficacy advantage of this lamp type is decreased and may be entirely lost compared to high pressure sodium lamps. Allegations that this also leads to higher amounts of light pollution from luminaires running these lamps arise principally because of older luminaires with poor shielding, still widely in use in the UK and in some other locations. Modern low-pressure sodium fixtures with better optics and full shielding, and the decreased skyglow impacts of yellow light preserve the luminous efficacy advantage of low-pressure sodium and result in most cases is less energy consumption and less visible light pollution. Unfortunately, due to continued lack of accurate information, many lighting professionals continue to disparage low-pressure sodium, contributing to its decreased acceptance and specification in lighting standards and therefore its use. Another disadvantage of low-pressure sodium lamps is that some people find the characteristic yellow light very displeasing aesthetically.
Because of the scatter of light by the atmosphere, different sources produce dramatically different amounts of skyglow from the same amount of light sent into the atmosphere.
In some cases, evaluation of existing plans has determined that more efficient lighting plans are possible. For instance, light pollution can be reduced by turning off unneeded outdoor lights, and only lighting stadiums when there are people inside. Timers are especially valuable for this purpose. One of the world's first coordinated legislative efforts to reduce the adverse effect of this pollution on the environment began in Flagstaff, Arizona, in the U.S. There, over three decades of ordinance development has taken place, with the full support of the population, often with government support, with community advocates, and with the help of major local observatories, including the United States Naval Observatory Flagstaff Station. Each component helps to educate, protect and enforce the imperatives to intelligently reduce detrimental light pollution.
One example of a lighting plan assessment can be seen in a report originally commissioned by the Office of the Deputy Prime Minister in the United Kingdom, and now available through the Department for Communities and Local Government. The report details a plan to be implemented throughout the UK, for designing lighting schemes in the countryside, with a particular focus on preserving the environment.
In another example, the city of Calgary has recently replaced most residential street lights with models that are comparably energy efficient. The motivation is primarily operation cost and environmental conservation. The costs of installation are expected to be regained through energy savings within six to seven years.
The Swiss Agency for Energy Efficiency (SAFE) uses a concept that promises to be of great use in the diagnosis and design of road lighting, "consommation électrique spécifique (CES)", which can be translated into English as "specific electric power consumption (SEC)". Thus, based on observed lighting levels in a wide range of Swiss towns, SAFE has defined target values for electric power consumption per metre for roads of various categories. Thus, SAFE currently recommends an SEC of 2 to 3 watts per meter for roads of less than 10 metre width (4 to 6 watts per metre for wider roads). Such a measure provides an easily applicable environmental protection constraint on conventional "norms", which usually are based on the recommendations of lighting manufacturing interests, who may not take into account environmental criteria. In view of ongoing progress in lighting technology, target SEC values will need to be periodically revised downwards.
A newer method for predicting and measuring various aspects of light pollution was described in the journal Lighting Research Technology (September 2008). Scientists at Rensselaer Polytechnic Institute's Lighting Research Center have developed a comprehensive method called Outdoor Site-Lighting Performance (OSP), which allows users to quantify, and thus optimize, the performance of existing and planned lighting designs and applications to minimize excessive or obtrusive light leaving the boundaries of a property. OSP can be used by lighting engineers immediately, particularly for the investigation of glow and trespass (glare analyses are more complex to perform and current commercial software does not readily allow them), and can help users compare several lighting design alternatives for the same site.
In the effort to reduce light pollution, researchers have developed a “Unified System of Photometry,” which is a way to measure how much or what kind of street lighting is needed. The Unified System of Photometry allows light fixtures to be designed to reduce energy use while maintaining or improving perceptions of visibility, safety, and security. There was a need to create a new system of light measurement at night because the biological way in which the eye’s rods and cones process light is different in nighttime conditions versus daytime conditions. Using this new system of photometry, results fro
In simple terms, we normally have two types of bulb colour available: Warm White & Day White (or Cool White).
What do they look like? Warm White best replaces existing halogen lighting because it has a warmer glow to it and a slightly yellow tint. This colour would match pretty closely to the light colour of an incandescent light bulb. Cool White or Day White produces a light which is very similar to daylight and can therefore have a slighty blue/purple tint. This color would match pretty closely to the light colour of fluorescent light.
Is the Warm White or the Daylight White a better light colour? While we have a lot of customers telling us that they prefer the Daylight white in a office environment to keep them alert, and the Warm White at home to feel more comfortable, it is mainly a personal preference.
To find a suitable replacement bulb, simply identify the bulb base that resembles the light bulb base you are looking to replace, and click on it. You will be presented with all of the bulbs we carry matching this base type. If you are unable to locate a suitable replacement light bulb please contact us and one of our associates will do their best to assist you.
|E27 Edison Screw||E26SKT|
|E5, E10||E11||E12||E14 Small Edison Screw|
|G17q, G17q-7, G17t-7, GX17q-7, GY17q|
|3 Screw Terminals|
|2 Slip-On Terminals|
|3 Contact Lugs|
A fluorescent lamp or fluorescent tube is a gas-discharge lamp that uses electricity to excite mercury vapor. The excited mercury atoms produce short-wave ultraviolet light that then causes a phosphor to fluoresce, producing visible light. A fluorescent lamp converts electrical power into useful light more efficiently than an incandescent lamp. Lower energy cost typically offsets the higher initial cost of the lamp. The lamp fixture is more costly because it requires a ballast to regulate the current through the lamp.
While larger fluorescent lamps have been mostly used in commercial or institutional buildings, the compact fluorescent lamp is now available in the same popular sizes as incandescents and is used as an energy-saving alternative in homes.
Fluorescent lamps are classified as hazardous waste and shouldn't be thrown in the trash. They must be recycled.
Fluorescence of certain rocks and other substances had been observed for hundreds of years before its nature was understood. By the middle of the 19th century, experimenters had observed a radiant glow emanating from partially evacuated glass vessels through which an electrical current passed. One of the first to explain it was the Irish scientist Sir George Stokes from the University of Cambridge, who named the phenomenon "fluorescence" after fluorite, a mineral many of whose samples fluoresce strongly due to impurities. The explanation relied on the nature of electricity and light phenomena as developed by the British scientists Michael Faraday and James Clerk Maxwell in the 1840s.
Little more was done with this phenomenon until 1856 when a German glassblower named Heinrich Geissler created a mercury vacuum pump that evacuated a glass tube to an extent not previously possible. When an electrical current passed through a Geissler tube, a strong green glow on the walls of the tube at the cathode end could be observed. Because it produced some beautiful light effects, the Geissler tube was a popular source of amusement. More important, however, was its contribution to scientific research. One of the first scientists to experiment with a Geissler tube was Julius Plücker who systematically described in 1858 the luminescent effects that occurred in a Geissler tube. He also made the important observation that the glow in the tube shifted position when in proximity to an electromagnetic field. Alexandre Edmond Becquerel observed in 1859 that certain substances gave off light when they were placed in a Geissler tube. He went on to apply thin coatings of luminescent materials to the surfaces of these tubes. Fluorescence occurred, but the tubes were very inefficient and had a short operating life.
Inquiries that began with the Geissler tube continued as even better vacuums were produced. The most famous was the evacuated tube used for scientific research by William Crookes. That tube was evacuated by the highly effective mercury vacuum pump created by Hermann Sprengel. Research conducted by Crookes and others ultimately led to the discovery of the electron in 1897 by J. J. Thomson. But the Crookes tube, as it came to be known, produced little light because the vacuum in it was too good and thus lacked the trace amounts of gas that are needed for electrically stimulated luminescence.
While Becquerel was primarily interested in conducting scientific research into fluorescence, Thomas Edison briefly pursued fluorescent lighting for its commercial potential. He invented a fluorescent lamp in 1896 that used a coating of calcium tungstate as the fluorescing substance, excited by X-rays, but although it received a patent in 1907, it was not put into production. As with a few other attempts to use Geissler tubes for illumination, it had a short operating life, and given the success of the incandescent light, Edison had little reason to pursue an alternative means of electrical illumination. Nikola Tesla made similar experiments in the 1890s, devising high frequency powered fluorescent bulbs that gave a bright greenish light, but as with Edison's devices, no commercial success was achieved.
Although Edison lost interest in fluorescent lighting, one of his former employees was able to create a gas-based lamp that achieved a measure of commercial success. In 1895 Daniel McFarlan Moore demonstrated lamps 2 to 3 meters (6.6 to 9.8 ft) in length that used carbon dioxide or nitrogen to emit white or pink light, respectively. As with future fluorescent lamps, they were considerably more complicated than an incandescent bulb.
After years of work, Moore was able to extend the operating life of the lamps by inventing an electromagnetically controlled valve that maintained a constant gas pressure within the tube. Although Moore’s lamp was complicated, expensive to install, and required very high voltages, it was considerably more efficient than incandescent lamps, and it produced a more natural light than incandescent lamps. From 1904 onwards Moore’s lighting system was installed in a number of stores and offices. Its success contributed to General Electric’s motivation to improve the incandescent lamp, especially its filament. GE’s efforts came to fruition with the invention of a tungsten-based filament. The extended lifespan of incandescent bulbs negated one of the key advantages of Moore’s lamp, but GE purchased the relevant patents in 1912. These patents and the inventive efforts that supported them were to be of considerable value when the firm took up fluorescent lighting more than two decades later.
At about the same time that Moore was developing his lighting system, another American was creating a means of illumination that also can be seen as a precursor to the modern fluorescent lamp. This was the mercury-vapor lamp, invented by Peter Cooper Hewitt and patented in 1901 (US 682692 )(Note: This patent number is universally misquoted as US889,692). Hewitt’s lamp luminesced when an electric current was passed through mercury vapor at a low pressure. Unlike Moore’s lamps, Hewitt's were manufactured in standardized sizes and operated at low voltages. The mercury-vapor lamp was superior to the incandescent lamps of the time in terms of energy efficiency, but the blue-green light it produced limited its applications. It was, however, used for photography and some industrial processes.
Mercury vapor lamps continued to be developed at a slow pace, especially in Europe, and by the early 1930s they received limited use for large-scale illumination. Some of them employed fluorescent coatings, but these were primarily used for color correction and not for enhanced light output. Mercury vapor lamps also anticipated the fluorescent lamp in their incorporation of a ballast to maintain a constant current.
Cooper-Hewitt had not been the first to use mercury vapor for illumination, as earlier efforts had been mounted by Way, Rapieff, Arons, and Bastian and Salisbury. Of particular importance was the mercury vapor lamp invented by Küch in Germany. This lamp used quartz in place of glass to allow higher operating temperatures, and hence greater efficiency. Although its light output relative to electrical consumption was better than other sources of light, the light it produced was similar to that of the Cooper-Hewitt lamp in that it lacked the red portion of the spectrum, making it unsuitable for ordinary lighting.
The next step in gas-based lighting took advantage of the luminescent qualities of neon, an inert gas that had been discovered in 1898 by isolation from the atmosphere. Neon glowed a brilliant red when used in Geissler tubes. By 1910, Georges Claude, a Frenchman who had developed a technology and a successful business for air liquefaction, was obtaining enough neon as a byproduct to support a neon lighting industry. While neon lighting was used around 1930 in France for general illumination, it was no more energy-efficient than conventional incandescent lighting. Neon tube lighting, which also includes the use of argon and mercury vapor as alternate gases, came to be used primarily for eye-catching signs and advertisements. Neon lighting was relevant to the development of fluorescent lighting, however, as Claude’s improved electrode (patented in 1915) overcame "sputtering", a major source of electrode degradation. Sputtering occurred when ionized particles struck an electrode and tore off bits of metal. Although Claude’s invention required electrodes with a lot of surface area, it showed that a major impediment to gas-based lighting could be overcome.
The development of the neon light also was significant for the last key element of the fluorescent lamp, its fluorescent coating. In 1926 Jacques Risler received a French patent for the application of fluorescent coatings to neon light tubes. The main use of these lamps, which can be considered the first commercially successful fluorescents, was for advertising, not general illumination. This, however, was not the first use of fluorescent coatings. As has been noted above, Edison used calcium tungstate for his unsuccessful lamp. Other efforts had been mounted, but all were plagued by low efficiency and various technical problems. Of particular importance was the invention in 1927 of a low-voltage “metal vapor lamp” by Friedrich Meyer, Hans-Joachim Spanner, and Edmund Germer, who were employees of a German firm in Berlin. A German patent was granted but the lamp never went into commercial production.
All the major features of fluorescent lighting were in place at the end of the 1920s. Decades of invention and development had provided the key components of fluorescent lamps: economically manufactured glass tubing, inert gases for filling the tubes, electrical ballasts, long-lasting electrodes, mercury vapor as a source of luminescence, effective means of producing a reliable electrical discharge, and fluorescent coatings that could be energized by ultraviolet light. At this point, intensive development was more important than basic research.
In 1934, Arthur Compton, a renowned physicist and GE consultant, reported to the GE lamp department on successful experiments with fluorescent lighting at General Electric Co., Ltd. in Great Britain (unrelated to General Electric in the United States). Stimulated by this report, and with all of the key elements available, a team led by George E. Inman built a prototype fluorescent lamp in 1934 at General Electric’s Nela Park (Ohio) engineering laboratory. This was not a trivial exercise; as noted by Arthur A. Bright, "A great deal of experimentation had to be done on lamp sizes and shapes, cathode construction, gas pressures of both argon and mercury vapor, colors of fluorescent powders, methods of attaching them to the inside of the tube, and other details of the lamp and its auxiliaries before the new device was ready for the public."
In addition to having engineers and technicians along with facilities for R&D work on fluorescent lamps, General Electric controlled what it regarded as the key patents covering fluorescent lighting, including the patents originally issued to Hewitt, Moore, and Küch. More important than these was a patent covering an electrode that did not disintegrate at the gas pressures that ultimately were employed in fluorescent lamps. Albert W. Hull of GE’s Schenectady Research Laboratory filed for a patent on this invention in 1927, which was issued in 1931.
While the Hull patent gave GE a basis for claiming legal rights over the fluorescent lamp, a few months after the lamp went into production the firm learned of a U.S. patent application that had been filed in 1927 for the aforementioned "metal vapor lamp" invented in Germany by Meyer, Spanner, and Germer. The patent application indicated that the lamp had been created as a superior means of producing ultraviolet light, but the application also contained a few statements referring to fluorescent illumination. Efforts to obtain a U.S. patent had met with numerous delays, but were it to be granted, the patent might have caused serious difficulties for GE. At first, GE sought to block the issuance of a patent by claiming that priority should go to one of their employees, Leroy J. Buttolph, who according to their claim had invented a fluorescent lamp in 1919 and whose patent application was still pending. GE also had filed a patent application in 1936 in Inman’s name to cover the “improvements” wrought by his group. In 1939 GE decided that the claim of Meyer, Spanner, and Germer had some merit, and that in any event a long interference procedure was not in their best interest. They therefore dropped the Buttolph claim and paid $180,000 to acquire the Meyer, et al. application, which at that point was owned by a firm known as Electrons, Inc. The patent was duly awarded in December 1939. This patent, along with the Hull patent, put GE on what seemed to be firm legal ground, although it faced years of legal challenges from Sylvania Electric Products, Inc., which claimed infringement on patents that it held.
Even though the patent issue would not be completely resolved for many years, General Electric’s strength in manufacturing and marketing the bulb gave it a pre-eminent position in the emerging fluorescent light market. Sales of "fluorescent lumiline lamps" commenced in 1938 when four different sizes of tubes were put on the market used in fixtures manufactured by three leading corporations, Lightolier, Artcraft Fluorescent Lighting Corporation, and Globe Lighting, two based in New York City. During the following year GE and Westinghouse publicized the new lights through exhibitions at the New York World’s Fair and the Golden Gate International Exposition in San Francisco. Fluorescent lighting systems spread rapidly during World War II as wartime manufacturing intensified lighting demand. By 1951 more light was produced in the United States by fluorescent lamps than by incandescent lamps.
In the first years zinc orthosilicate with varying content of beryllium was used as greenish phosphor. Small additions of magnesium tungstate improved the blue part of the spectrum yielding acceptable white. After it was discovered that beryllium was toxic halophosphate based phosphors took over.
The fundamental means for conversion of electrical energy into radiant energy in a fluorescent lamp relies on inelastic scattering of electrons. An incident electron collides with an atom in the gas. If the free electron has enough kinetic energy, it transfers energy to the atom's outer electron, causing that electron to temporarily jump up to a higher energy level. The collision is 'inelastic' because a loss of energy occurs.
This higher energy state is unstable, and the atom will emit an ultraviolet photon as the atom's electron reverts to a lower, more stable, energy level. Most of the photons that are released from the mercury atoms have wavelengths in the ultraviolet (UV) region of the spectrum, predominantly at wavelengths of 253.7 nm and 185 nm. These are not visible to the human eye, so they must be converted into visible light. This is done by making use of fluorescence. Ultraviolet photons are absorbed by electrons in the atoms of the lamp's interior fluorescent coating, causing a similar energy jump, then drop, with emission of a further photon. The photon that is emitted from this second interaction has a lower energy than the one that caused it. The chemicals that make up the phosphor are chosen so that these emitted photons are at wavelengths visible to the human eye. The difference in energy between the absorbed ultra-violet photon and the emitted visible light photon goes toward heating up the phosphor coating.
When the light is turned on, the electric power heats up the cathode enough for it to emit electrons. These electrons collide with and ionize noble gas atoms inside the bulb surrounding the filament to form a plasma by the process of impact ionization. As a result of avalanche ionization, the conductivity of the ionized gas rapidly rises, allowing higher currents to flow through the lamp.
A fluorescent lamp tube is filled with a gas containing low pressure mercury vapor and argon, xenon, neon, or krypton. The pressure inside the lamp is around 0.3% of atmospheric pressure. The inner surface of the bulb is coated with a fluorescent (and often slightly phosphorescent) coating made of varying blends of metallic and rare-earth phosphor salts. The bulb's electrodes are typically made of coiled tungsten and usually referred to as cathodes because of their prime function of emitting electrons. For this, they are coated with a mixture of barium, strontium and calcium oxides chosen to have a low thermionic emission temperature.
Fluorescent lamp tubes are typically straight and range in length from about 100 millimeters (3.9 in) for miniature lamps, to 2.43 meters (8.0 ft) for high-output lamps. Some lamps have the tube bent into a circle, used for table lamps or other places where a more compact light source is desired. Larger U-shaped lamps are used to provide the same amount of light in a more compact area, and are used for special architectural purposes. Compact fluorescent lamps have several small-diameter tubes joined in a bundle of two, four, or six, or a small diameter tube coiled into a spiral, to provide a high amount of light output in little volume.
Light-emitting phosphors are applied as a paint-like coating to the inside of the tube. The organic solvents are allowed to evaporate, then the tube is heated to nearly the melting point of glass to drive off remaining organic compounds and fuse the coating to the lamp tube. Careful control of the grain size of the suspended phosphors is necessary; large grains, 35 micrometers or larger, lead to weak grainy coatings, whereas too many small particles 1 or 2 micrometers or smaller leads to poor light maintenance and efficiency. Most phosphors perform best with a particle size around 10 micrometers. The coating must be thick enough to capture all the ultraviolet light produced by the mercury arc, but not so thick that the phosphor coating absorbs too much visible light. The first phosphors were synthetic versions of naturally occurring fluorescent minerals, with small amounts of metals added as activators. Later other compounds were discovered, allowing differing colors of lamps to be made.
Fluorescent lamps are negative differential resistance devices, so as more current flows through them (measured in amperes), the electrical resistance of the fluorescent lamp drops, allowing even more current to flow. Connected directly to a constant-voltage power supply, a fluorescent lamp would instantly be destructed by too much current flow. To prevent this, fluorescent lamps must use an auxiliary device, a ballast, to limit the current flow through the tube.
The terminal voltage across an operating lamp varies depending on the arc current, tube diameter, temperature, and fill gas. A fixed part of the voltage drop is due to the electrodes. A general lighting service T12 48 inch (1200 mm) lamp operates at 430 mA, with 100 volts drop. High output lamps operate at 800 mA, and some types operate up to 1500 mA. The power level varies from 10 watts per foot (33 watts per meter) to 25 watts per foot (82 watts per meter) of tube length for T12 lamps.
The simplest ballast for alternating current use is an inductor placed in series, consisting of a winding on a laminated magnetic core. The inductance of this winding limits the flow of AC current. This type is still used, for example, in 120 volt operated desk lamps using relatively short lamps. Ballasts are rated for the size of lamp and power frequency. Where the mains voltage is insufficient to start long fluorescent lamps, the ballast is often a step-up autotransformer with substantial leakage inductance (so as to limit the current flow). Either form of inductive ballast may also include a capacitor for power factor correction.
Many different circuits have been used to operate fluorescent lamps. The choice of circuit is based on mains voltage, tube length, initial cost, long term cost, instant versus non-instant starting, temperature ranges and parts availability, etc.
Fluorescent lamps can run directly from a DC supply of sufficient voltage to strike an arc. The ballast must be resistive, and would consume about as much power as the lamp. When operated from DC, the starting switch is often arranged to reverse the polarity of the supply to the lamp each time it is started; otherwise, the mercury accumulates at one end of the tube. Fluorescent lamps are (almost) never operated directly from DC for those reasons. Instead, an inverter converts the DC into AC and provides the current-limiting function as described below for electronic ballasts.
The light output and performance of fluorescent lamps is critically affected by the temperature of the bulb wall and its effect on the partial pressure of mercury vapor within the lamp. Each lamp contains a small amount of mercury, which must vaporize to support the lamp current and generate light. At low temperatures the mercury is in the form of dispersed liquid droplets. As the lamp warms, more of the mercury is in vapor form. At higher temperatures, self-absorption in the vapor reduces the yield of UV and visible light. Since mercury condenses at the coolest spot in the lamp, careful design is required to maintain that spot at the optimum temperature, around 40 °C.
By using an amalgam with some other metal, the vapor pressure is reduced and the optimum temperature range extended upward; however, the bulb wall "cold spot" temperature must still be controlled to prevent migration of the mercury out of the amalgam and condensing on the cold spot. Fluorescent lamps intended for higher output will have structural features such as a deformed tube or internal heat-sinks to control cold spot temperature and mercury distribution. Heavily loaded small lamps, such as compact fluorescent lamps, also include heat-sink areas in the tube to maintain mercury vapor pressure at the optimum value.
The efficiency of fluorescent lighting owes much to the fact that low pressure mercury discharges emit about 65% of their total light in the 254 nm line (another 10–20% of the light is emitted in the 185 nm line). The UV light is absorbed by the bulb's fluorescent coating, which re-radiates the energy at longer wavelengths to emit visible light. The blend of phosphors controls the color of the light, and along with the bulb's glass prevents the harmful UV light from escaping.
Only a fraction of the electrical energy input into a lamp gets turned into useful light. The ballast dissipates some heat; electronic ballasts may be around 90% efficient. A fixed voltage drop occurs at the electrodes. Some of the energy in the mercury vapor column is also dissipated, but about 85% is turned into visible and ultraviolet light.
Not all the UV energy on the phosphor gets converted into visible light. In a modern lamp, for every 100 incident photons of UV impacting the phosphor, only 86 visible light photons are emitted (a quantum efficiency of 86%). The largest single loss in modern lamps is due to the lower energy of each photon of visible light, compared to the energy of the UV photons that generated them. Incident photons have an energy of 5.5 electron volts but produce visible light photons with energy around 2.5 electron volts, so only 45% of the UV energy is used. If a so-called "two-photon" phosphor could be developed, this would improve the efficiency but much research has not yet found such a system.
Most fluorescent lamps use electrodes that operate in thermionic emission mode, meaning they are operated at a high enough temperature for the chosen material (normally a special coating) to liberate electrons across to the gas-fill by heat.
However, there are also tubes that operate in cold cathode mode, whereby electrons are liberated only by the level of potential difference provided. This does not mean the electrodes are cold (and indeed, they can be very hot), but it does mean they are operating below their thermionic emission temperature. Because cold cathode lamps have no thermionic emission coating to wear out they can have much longer lives than is commonly available with thermionic emission tubes. This quality makes them desirable for maintenance-free long-life applications (such as LCD backlight displays). Sputtering of the electrode may still occur, but electrodes can be shaped (e.g. into an internal cylinder) to capture most of the sputtered material so it is not lost from the electrode.
Cold cathode lamps are generally less efficient than thermionic emission lamps because the cathode fall voltage is much higher. The increased fall voltage results in more power dissipation at tube ends, which does not contribute to light output. However, this is less significant with longer tubes. The increased power dissipation at tube ends also usually means cold cathode tubes have to be run at a lower loading than their thermionic emission equivalents. Given the higher tube voltage required anyway, these tubes can easily be made long, and even run as series strings. They are better suited for bending into special shapes for lettering and signage, and can also be instantly switched on or off.
The mercury atoms in the fluorescent tube must be ionized before the arc can "strike" within the tube. For small lamps, it does not take much voltage to strike the arc and starting the lamp presents no problem, but larger tubes require a substantial voltage (in the range of a thousand volts).
This technique uses a combination filament/cathode at each end of the lamp in conjunction with a mechanical or automatic switch (see circuit diagram to the right) that initially connect the filaments in series with the ballast and thereby preheat the filaments prior to striking the arc. Note that in North America, this is referred to as Preheat. Elsewhere this is referred to as Switchstart.
These systems are standard equipment in 200–240 V countries (and for 100–120 V lamps up to about 30 watts), and generally use a glow starter. Before the 1960s, four-pin thermal starters and manual switches were also used. Electronic starters are also sometimes used with these electromagnetic ballast lamp fittings.
The automatic glow starter shown in the photograph to the left consists of a small gas-discharge tube, containing neon and/or argon and fitted with a bi-metallic electrode. The special bi-metallic electrode is the key to the automatic starting mechanism.
When power is first applied to the lamp circuit, a glow discharge will appear over the electrodes of the starter. This glow discharge will heat the gas in the starter and cause the bi-metallic electrode to bend towards the other electrode. When the electrodes touch, the two filaments of the fluorescent lamp and the ballast will effectively be switched in series to the supply voltage. This causes the filaments to glow and emit electrons into the gas column by thermionic emission. In the starter's tube, the touching electrodes have stopped the glow discharge, causing the gas to cool down again. The bi-metallic electrode also cools down and starts to move back. When the electrodes separate, the inductive kick from the ballast provides the high voltage to start the lamp. The starter additionally has a capacitor wired in parallel to its gas-discharge tube, in order to prolong the electrode life.
Once the tube is struck, the impinging main discharge then keeps the cathode hot, permitting continued emission without the need for the starter to close. The starter does not close again because the voltage across the lit tube is insufficient to start a glow discharge in the starter.
Tube strike is reliable in these systems, but glow starters will often cycle a few times before allowing the tube to stay lit, which causes undesirable flashing during starting. (The older thermal starters behaved better in this respect.)
If the tube fails to strike, or strikes but then extinguishes, the starting sequence is repeated. With automated starters such as glow starters, a failing tube will cycle endlessly, flashing as the lamp quickly goes out because emission mix is insufficient to keep the lamp current high enough to keep the glow starter open. This causes flickering, and runs the ballast at above design temperature. Some more advanced starters time out in this situation, and do not attempt repeated starts until power is reset. Some older systems used a thermal over-current trip to detect repeated starting attempts. These require manual reset.
Electronic starters use a more complex method to preheat the cathodes of a fluorescent lamp. Electronic starters are made in the same physical case as glow starters for direct replacement. They commonly use a specially designed semiconductor switch. They are programmed with a predefined preheat time to ensure that the cathodes are fully heated and reduce the amount of sputtered emission mix to prolong the life of the lamp; typically it is claimed that the life of a lamp frequently switched on, as in domestic use, is prolonged by a factor of 3 to 4 times. Start time is typically 1 to 4 seconds. Electronic starters contain a series of capacitors that are capable of producing a high voltage pulse of electricity across the lamp to ensure that it strikes correctly. Electronic starters only attempt to start a lamp for a short time when power is initially applied and will not repeatedly attempt to restrike a lamp that is dead and cannot sustain an arc; some will automatically shut down a failed lamp. This eliminates the re-striking of a lamp and the continuous flickering on and off of a failing lamp with a glow starter. Some fast-start electronic starters can strike the fluorescent tube within 0.3 seconds.
In some cases, a high voltage is applied directly: instant start fluorescent tubes simply use a high enough voltage to break down the gas and mercury column and thereby start arc conduction. These tubes can be identified by a single pin at each end of the tube. The lamp holders have a "disconnect" socket at the low-voltage end to isolate the ballast and prevent electric shock. Low-cost lighting fixtures with an integrated electronic ballast use instant start on preheat lamps, even if it reduces the lamp lifespan.
Newer rapid start ballast designs provide filament power windings within the ballast; these rapidly and continuously warm the filaments/cathodes using low-voltage AC. No inductive voltage spike is produced for starting, so the lamps must be mounted near a grounded (earthed) reflector to allow the glow discharge to propagate through the tube and initiate the arc discharge. In some lamps a grounded "starting aid" strip is attached to the outside of the lamp glass.
Quick-start ballasts use a small auto-transformer to heat the filaments when power is first applied. When an arc strikes, the filament heating power is reduced and the tube will start within half a second. The auto-transformer is either combined with the ballast or may be a separate unit. Tubes need to be mounted near an earthed metal reflector in order for them to strike. Quick-start ballasts were more common in commercial installations because of lower maintenance as no starter switches need to be replaced. They are also used in domestic installations due to the virtually instant start. Quick-start ballasts are only used on 240 V circuits and are designed for use with the older, less-efficient T12 tubes, T8 retrofits will not start when used with quick-start ballasts.
Semi-resonant start was invented by Thorn Lighting for use with T12 fluorescent tubes. This method uses a double wound transformer and a capacitor. With no arc current, the transformer and capacitor ring at mains frequency and generate about twice mains voltage across the tube, and a small electrode heating current. This tube voltage is too low to strike the arc with cold electrodes, but as the electrodes heat up to thermionic emission temperature, the tube striking voltage reduces below that of the ringing voltage, and the arc strikes. As the electrodes heat, the lamp slowly, over 3–5 seconds, reaches full brightness. As the arc current increases and tube voltage drops, the circuit provides current limiting.
Semi-resonant start was mainly used in commercial installations because of their higher initial cost. There are no starter switches to be replaced and cathode damage is reduced during starting. Due to the high open circuit tube voltage, this starting method was particularly good for starting tubes in cold locations. Additionally, the circuit power factor is almost 1.0, and no additional power factor correction is needed in the lighting installation. As the design requires that twice the mains voltage must be lower than the cold-cathode striking voltage (or the tubes would erroneously instant-start), this design can only be used with 5 ft and longer tubes on 240 V mains. Semi-resonant start fixtures are generally incompatible with energy saving T8 retrofit tubes, because such tubes have a higher starting voltage than T12 lamps and may not start reliably,especially in low temperatures. Recent proposals in some countries to phase out T12 tubes will reduce the application of this starting method.
This is used with electronic ballasts shown below. A programmed-start ballast is a more advanced version of rapid start. This ballast applies power to the filaments first, then after a short delay to allow the cathodes to preheat, applies voltage to the lamps to strike an arc. This ballast gives the best life and most starts from lamps, and so is preferred for applications with very frequent power cycling such as vision examination rooms and restrooms with a motion detector switch.
Electronic ballasts employ transistors to alter mains voltage frequency into high-frequency AC while also regulating the current flow in the lamp. These ballasts take advantage of the higher efficacy of lamps operated with higher-frequency current. Efficacy of a fluorescent lamp rises by almost 10% at a frequency of 10 kHz, compared to efficacy at normal power frequency. When the AC period is shorter than the relaxation time to de-ionize mercury atoms in the discharge column, the discharge stays closer to optimum operating condition. Electronic ballasts typically work in rapid start or instant start mode. Electronic ballasts are commonly supplied with AC power, which is internally converted to DC and then back to a variable frequency AC waveform. Depending upon the capacitance and the quality of constant-current pulse-width modulation, this can largely eliminate modulation at 100 or 120 Hz.
Low cost ballasts mostly contain only a simple oscillator and series resonant LC circuit. When turned on, the oscillator starts, and the LC circuit charges. After a short time the voltage across the lamp reaches about 1 kV and the lamp ignites. The process is too fast to preheat the cathodes, so the lamp instant-starts in cold cathode mode. The cathode filaments are still used for protection of the ballast from overheating if the lamp does not ignite. A few manufacturers use positive temperature coefficient (PTC) thermistors to disable instant starting and give some time to preheat the filaments.
More complex electronic ballasts use programmed start. The output AC frequency is started above the resonance frequency of the output circuit of the ballast; and after the filaments are heated, the frequency is rapidly decreased. If the frequency approaches the resonant frequency of the ballast, the output voltage will increase so much that the lamp will ignite. If the lamp does not ignite, an electronic circuit stops the operation of the ballast.
Many electronic ballasts are controlled by a microcontroller or similar, and these are sometimes called digital ballasts. Digital ballasts can apply quite complex logic to lamp starting and operation. This enables functions such as testing for broken electrodes and missing tubes before attempting to start, auto detect tube replacement, and auto detection of tube type, such that a single ballast can be used with several different tubes, even those that operate at different arc currents, etc. Once such fine grained control over the starting and arc current is achievable, features such as dimming, and having the ballast maintain a constant light level against changing sunlight contribution are all easily included in the embedded microcontroller software, and can be found in various manufacturers' products.
Since introduction in the 1990s, high frequency ballasts have been used in general lighting fixtures with either rapid start or pre-heat lamps. These ballasts convert the incoming power to an output frequency in excess of 20 kHz. This increases lamp efficiency. These are used in several applications, including new generation tanning lamp systems, whereby a 100 watt lamp (e.g., F71T12BP) can be lit using 65 to 70 watts of actual power while obtaining the same luminous flux (measured in lumens) as magnetic ballasts. These ballasts operate with voltages that can be almost 600 volts, requiring some consideration in housing design, and can cause a minor limitation in the length of the wire leads from the ballast to the lamp ends.
The end of life failure mode for fluorescent lamps varies depending on how they are used and their control gear type. Often the light will turn pink (see section 2.7.4) with black burns on the ends of the bulb due to sputtering of emission mix (see below). The lamp may also flicker at a noticeable rate (see section 6.8). More information about other normal tube failure modes including the above are as follows:
The "emission mix" on the tube filaments/cathodes is necessary to enable electrons to pass into the gas via thermionic emission at the tube operating voltages used. The mix is slowly sputtered off by bombardment with electrons and mercury ions during operation, but a larger amount is sputtered off each time the tube is started with cold cathodes. The method of starting the lamp has a significant impact on this. Lamps operated for typically less than 3 hours each switch-on will normally run out of the emission mix before other parts of the lamp fail. The sputtered emission mix forms the dark marks at the tube ends seen in old tubes. When all the emission mix is gone, the cathode cannot pass sufficient electrons into the gas fill to maintain the discharge at the designed tube operating voltage. Ideally, the control gear should shut down the tube when this happens. However, some control gear will provide sufficient increased voltage to continue operating the tube in cold cathode mode, which will cause overheating of the tube end (visible as orange swivelling arcs) and rapid disintegration of the electrodes (filament goes open-circuit) and filament support wires until they are completely gone or the glass cracks, wrecking the low pressure gas fill and stopping the gas discharge. This is sometimes referred to as "loss of vacuum" and is sometimes audible as a "pop" then a "hiss" as the low pressure gas fill is wrecked due to the cracked glass allowing air to enter like in a puncture which can also cause filament evaporation.
This may occur in compact fluorescent lamps with integral electrical ballasts or in linear lamps. Ballast electronics failure is a somewhat random process that follows the standard failure profile for any electronic device. There is an initial small peak of early failures, followed by a drop and steady increase over lamp life. Life of electronics is heavily dependent on operating temperature—it typically halves for each 10 °C temperature rise. The quoted average life of a lamp is usually at 25 °C ambient (this may vary by country). The average life of the electronics at this temperature is normally greater than this, so at this temperature, not many lamps will fail due to failure of the electronics. In some fittings, the ambient temperature could be well above this, in which case failure of the electronics may become the predominant failure mechanism. Similarly, running a compact fluorescent lamp base-up will result in hotter electronics, which can cause shorter average life (particularly with higher power rated ones). Electronic ballasts should be designed to shut down the tube when the emission mix runs out as described above. In the case of integral electronic ballasts, since they never have to work again, this is sometimes done by having them deliberately burn out some component to permanently cease operation.
In most CFLs the filaments are connected in series, with a small capacitor between them. The discharge, once lit, is in parallel to the capacitor and presents a lower-resistance path, effectively shorting the capacitor out. One of the most common failure modes of cheap lamps is caused by underrating this capacitor (using lower-voltage, lower-cost part), which is very stressed during operation, leading to its premature failure.
The phosphor drops off in efficiency during use. By around 25,000 operating hours, it will typically be half the brightness of a new lamp (although some manufacturers claim much longer half-lives for their lamps). Lamps that do not suffer failures of the emission mix or integral ballast electronics will eventually develop this failure mode. They still work, but have become dim and inefficient. The process is slow, and often only becomes obvious when a new lamp is operating next to an old one.
Like in all mercury-based gas-filled tubes, mercury is slowly absorbed into glass, phosphor, and tube electrodes throughout the lamp life, where it can no longer function. Newer lamps now have just enough mercury to last the expected life of the lamp. Loss of mercury will take over from failure of the phosphor in some lamps. The failure symptoms are similar, except loss of mercury initially causes an extended run-up time to full light output, and finally causes the lamp to glow a dim pink when the mercury runs out and the argon base gas takes over as the primary discharge.This page was: Helpful | Not Helpful
Thomas Alva Edison (February 11, 1847 – October 18, 1931) was an American inventor, scientist, and businessman who developed many devices that greatly influenced life around the world, including the phonograph, the motion picture camera, and a long-lasting, practical electric light bulb. Dubbed "The Wizard of Menlo Park" (now Edison, New Jersey) by a newspaper reporter, he was one of the first inventors to apply the principles of mass production and large teamwork to the process of invention, and therefore is often credited with the creation of the first industrial research laboratory.
Edison is the third most prolific inventor in history, holding 1,093 US patents in his name, as well as many patents in the United Kingdom, France, and Germany. He is credited with numerous inventions that contributed to mass communication and, in particular, telecommunications. These included a stock ticker, a mechanical vote recorder, a battery for an electric car, electrical power, recorded music and motion pictures. His advanced work in these fields was an outgrowth of his early career as a telegraph operator. Edison originated the concept and implementation of electric-power generation and distribution to homes, businesses, and factories – a crucial development in the modern industrialized world. His first power station was on Manhattan Island, New York.
Thomas Edison was born in Milan, Ohio, and grew up in Port Huron, Michigan. He was the seventh and last child of Samuel Ogden Edison, Jr. (1804–96, born in Marshalltown, Nova Scotia, Canada) and Nancy Matthews Elliott (1810–1871, born in Chenango County, New York). His father had to escape from Canada because he took part in the unsuccessful Mackenzie Rebellion of 1837. Edison considered himself to be of Dutch ancestry.
In school, the young Edison's mind often wandered, and his teacher, the Reverend Engle, was overheard calling him "addled". This ended Edison's three months of official schooling. Edison recalled later, "My mother was the making of me. She was so true, so sure of me; and I felt I had something to live for, someone I must not disappoint." His mother homeschooled him. Much of his education came from reading R.G. Parker's School of Natural Philosophy and The Cooper Union.
Edison developed hearing problems at an early age. The cause of his deafness has been attributed to a bout of scarlet fever during childhood and recurring untreated middle-ear infections. Around the middle of his career Edison attributed the hearing impairment to being struck on the ears by a train conductor when his chemical laboratory in a boxcar caught fire and he was thrown off the train in Smiths Creek, Michigan, along with his apparatus and chemicals. In his later years he modified the story to say the injury occurred when the conductor, in helping him onto a moving train, lifted him by the ears.
Edison's family was forced to move to Port Huron, Michigan, when the railroad bypassed Milan in 1854, but his life there was bittersweet. He sold candy and newspapers on trains running from Port Huron to Detroit, and he sold vegetables to supplement his income. This began Edison's long streak of entrepreneurial ventures as he discovered his talents as a businessman. These talents eventually led him to found 14 companies, including General Electric, which is still in existence as one of the largest publicly traded companies in the world.
Edison became a telegraph operator after he saved three-year-old Jimmie MacKenzie from being struck by a runaway train. Jimmie's father, station agent J.U. MacKenzie of Mount Clemens, Michigan, was so grateful that he trained Edison as a telegraph operator. Edison's first telegraphy job away from Port Huron was at Stratford Junction, Ontario, on the Grand Trunk Railway. In 1866, at the age of 19, Thomas Edison moved to Louisville, Kentucky, where, as an employee of Western Union, he worked the Associated Press bureau news wire. Edison requested the night shift, which allowed him plenty of time to spend at his two favorite pastimes—reading and experimenting. Eventually, the latter pre-occupation cost him his job. One night in 1867, he was working with a lead-acid battery when he spilled sulfuric acid onto the floor. It ran between the floorboards and onto his boss's desk below. The next morning Edison was fired.
One of his mentors during those early years was a fellow telegrapher and inventor named Franklin Leonard Pope, who allowed the impoverished youth to live and work in the basement of his Elizabeth, New Jersey home. Some of Edison's earliest inventions were related to telegraphy, including a stock ticker. His first patent was for the electric vote recorder, (U. S. Patent 90,646), which was granted on June 1, 1869.
On December 25, 1871, Edison married 16-year-old Mary Stilwell, whom he had met two months earlier as she was an employee at one of his shops. They had three children:
Mary Edison died on August 9, 1884, possibly from a brain tumor.
On February 24, 1886, at the age of thirty nine, Edison married 20-year-old Mina Miller in Akron, Ohio. She was the daughter of inventor Lewis Miller, co-founder of the Chautauqua Institution and a benefactor of Methodist charities. They also had three children:
Mina outlived Thomas Edison, dying on August 24, 1947.
Mary Had a Little Lamb
Thomas Edison reciting "Mary Had a Little Lamb"
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Thomas Edison began his career as an inventor in Newark, New Jersey, with the automatic repeater and his other improved telegraphic devices, but the invention which first gained him notice was the phonograph in 1877. This accomplishment was so unexpected by the public at large as to appear almost magical. Edison became known as "The Wizard of Menlo Park," New Jersey. His first phonograph recorded on tinfoil around a grooved cylinder, but had poor sound quality and the recordings could only be played a few times. In the 1880s, a redesigned model using wax-coated cardboard cylinders was produced by Alexander Graham Bell, Chichester Bell, and Charles Tainter. This was one reason that Thomas Edison continued work on his own "Perfected Phonograph."
Edison's major innovation was the first industrial research lab, which was built in Menlo Park, New Jersey. It was built with the funds from the sale of Edison's quadruplex telegraph. After his demonstration of the telegraph, Edison was not sure that his original plan to sell it for $4,000 to $5,000 was right, so he asked Western Union to make a bid. He was surprised to hear them offer $10,000, which he gratefully accepted. The quadruplex telegraph was Edison's first big financial success, and Menlo Park became the first institution set up with the specific purpose of producing constant technological innovation and improvement. Edison was legally attributed with most of the inventions produced there, though many employees carried out research and development under his direction. His staff was generally told to carry out his directions in conducting research, and he drove them hard to produce results.
William J. Hammer, a consulting electrical engineer, began his duties as a laboratory assistant to Edison in December 1879. He assisted in experiments on the telephone, phonograph, electric railway, iron ore separator, electric lighting, and other developing inventions. However, Hammer worked primarily on the incandescent electric lamp and was put in charge of tests and records on that device. In 1880, he was appointed chief engineer of the Edison Lamp Works. In his first year, the plant under General Manager Francis Robbins Upton turned out 50,000 lamps. According to Edison, Hammer was "a pioneer of incandescent electric lighting".
Nearly all of Edison's patents were utility patents, which were protected for a 17-year period and included inventions or processes that are electrical, mechanical, or chemical in nature. About a dozen were design patents, which protect an ornamental design for up to a 14-year period. As in most patents, the inventions he described were improvements over prior art. The phonograph patent, in contrast, was unprecedented as describing the first device to record and reproduce sounds. Edison did not invent the first electric light bulb, but instead invented the first commercially practical incandescent light. Many earlier inventors had previously devised incandescent lamps including Henry Woodward, and Mathew Evans. Others who developed early and not commercially practical incandescent electric lamps included Humphry Davy, James Bowman Lindsay, Moses G. Farmer, William E. Sawyer, Joseph Swan and Heinrich Göbel. Some of these early bulbs had such flaws as an extremely short life, high expense to produce, and high electric current drawn, making them difficult to apply on a large scale commercially. In 1878, Edison applied the term filament to the element of glowing wire carrying the current, although the English inventor Joseph Swan had used the term prior to this. Swan developed an incandescent light with a long lasting filament at about the same time as Edison, as Swan's earlier bulbs lacked the high resistance needed to be an effective part of an electrical utility. Edison and his co-workers set about the task of creating longer-lasting bulbs. In Britain, Joseph Swan had been able to obtain a patent on the incandescent lamp because although he had been making successful lamps some time before Edison was tardy in applying for patents so application was submitted by Edison but failed due to an oversight in the drafting of Edison's patent application. Unable to raise the required capital in Britain because of this, Edison was forced to enter into a joint venture with Swan (known as Ediswan). Swan acknowledged that Edison had anticipated him, saying "Edison is entitled to more than I ... he has seen further into this subject, vastly than I, and foreseen and provided for details that I did not comprehend until I saw his system". By 1879, Edison had produced a new concept: a high resistance lamp in a very high vacuum, which would burn for hundreds of hours. While the earlier inventors had produced electric lighting in laboratory conditions, dating back to a demonstration of a glowing wire by Alessandro Volta in 1800, Edison concentrated on commercial application, and was able to sell the concept to homes and businesses by mass-producing relatively long-lasting light bulbs and creating a complete system for the generation and distribution of electricity.
In just over a decade Edison's Menlo Park laboratory had expanded to occupy two city blocks. Edison said he wanted the lab to have "a stock of almost every conceivable material". A newspaper article printed in 1887 reveals the seriousness of his claim, stating the lab contained "eight thousand kinds of chemicals, every kind of screw made, every size of needle, every kind of cord or wire, hair of humans, horses, hogs, cows, rabbits, goats, minx, camels ... silk in every texture, cocoons, various kinds of hoofs, shark's teeth, deer horns, tortoise shell ... cork, resin, varnish and oil, ostrich feathers, a peacock's tail, jet, amber, rubber, all ores ..." and the list goes on.
Over his desk, Edison displayed a placard with Sir Joshua Reynolds' famous quotation: "There is no expedient to which a man will not resort to avoid the real labor of thinking." This slogan was reputedly posted at several other locations throughout the facility.
With Menlo Park, Edison had created the first industrial laboratory concerned with creating knowledge and then controlling its application.
In 1877–78, Edison invented and developed the carbon microphone used in all telephones along with the Bell receiver until the 1980s. After protracted patent litigation, in 1892 a federal court ruled that Edison—and not Emile Berliner—was the inventor of the carbon microphone. The carbon microphone was also used in radio broadcasting and public address work through the 1920s.
Building on the contributions of other developers over the previous three quarters of a century, Edison made significant improvements to the idea of incandescent light, and wound up in the public consciousness as "the inventor" of the lightbulb.
After many experiments with platinum and other metal filaments, Edison returned to a carbon filament. The first successful test was on October 22, 1879; it lasted 40 hours. Edison continued to improve this design and by November 4, 1879, filed for U.S. patent 223,898 (granted on January 27, 1880) for an electric lamp using "a carbon filament or strip coiled and connected to platina contact wires". Although the patent described several ways of creating the carbon filament including "cotton and linen thread, wood splints, papers coiled in various ways", it was not until several months after the patent was granted that Edison and his team discovered a carbonized bamboo filament that could last over 1,200 hours. The idea of using this particular raw material originated from Edison's recalling his examination of a few threads from a bamboo fishing pole while relaxing on the shore of Battle Lake in the present-day state of Wyoming, where he and other members of a scientific team had traveled so that they could clearly observe a total eclipse of the sun on July 29, 1878, from the Continental Divide.
In 1878, Edison formed the Edison Electric Light Company in New York City with several financiers, including J. P. Morgan and the members of the Vanderbilt family. Edison made the first public demonstration of his incandescent light bulb on December 31, 1879, in Menlo Park. It was during this time that he said: "We will make electricity so cheap that only the rich will burn candles."
Lewis Latimer joined the Edison Electric Light Company in 1884. Latimer had received a patent in January 1881 for the "Process of Manufacturing Carbons", an improved method for the production of carbon filaments for lightbulbs. Latimer worked as an engineer, a draftsman and an expert witness in patent litigation on electric lights.
George Westinghouse's company bought Philip Diehl's competing induction lamp patent rights (1882) for $25,000, forcing the holders of the Edison patent to charge a more reasonable rate for the use of the Edison patent rights and lowering the price of the electric lamp.
On October 8, 1883, the US patent office ruled that Edison's patent was based on the work of William Sawyer and was therefore invalid. Litigation continued for nearly six years, until October 6, 1889, when a judge ruled that Edison's electric light improvement claim for "a filament of carbon of high resistance" was valid. To avoid a possible court battle with Joseph Swan, whose British patent had been awarded a year before Edison's, he and Swan formed a joint company called Ediswan to manufacture and market the invention in Britain.
Mahen Theatre in Brno in what is now the Czech Republic, was the first public building in the world to use Edison's electric lamps, with the installation supervised by Edison's assistant in the invention of the lamp, Francis Jehl. In September 2010, a sculpture of three giant light bulbs was erected in Brno, in front of the theatre.
Edison patented a system for electricity distribution in 1880, which was essential to capitalize on the invention of the electric lamp. On December 17, 1880, Edison founded the Edison Illuminating Company. The company established the first investor-owned electric utility in 1882 on Pearl Street Station, New York City. It was on September 4, 1882, that Edison switched on his Pearl Street generating station's electrical power distribution system, which provided 110 volts direct current (DC) to 59 customers in lower Manhattan.
Earlier in the year, in January 1882 he had switched on the first steam generating power station at Holborn Viaduct in London. The DC supply system provided electricity supplies to street lamps and several private dwellings within a short distance of the station. On January 19, 1883, the first standardized incandescent electric lighting system employing overhead wires began service in Roselle, New Jersey.
Edison's true success, like that of his friend Henry Ford, was in his ability to maximize profits through establishment of mass-production systems and intellectual property rights. George Westinghouse and Edison became adversaries because of Edison's promotion of direct current (DC) for electric power distribution instead of the more easily transmitted alternating current (AC) system invented by Nikola Tesla and promoted by Westinghouse. Unlike DC, AC could be stepped up to very high voltages with transformers, sent over thinner and cheaper wires, and stepped down again at the destination for distribution to users.
In 1887 there were 121 Edison power stations in the United States delivering DC electricity to customers. When the limitations of DC were discussed by the public, Edison launched a propaganda campaign to convince people that AC was far too dangerous to use. The problem with DC was that the power plants could economically deliver DC electricity only to customers within about one and a half miles (about 2.4 km) from the generating station, so that it was suitable only for central business districts. When George Westinghouse suggested using high-voltage AC instead, as it could carry electricity hundreds of miles with marginal loss of power, Edison waged a "War of Currents" to prevent AC from being adopted.
The war against AC led him to become involved in the development and promotion of the electric chair (using AC) as an attempt to portray AC to have greater lethal potential than DC. Edison went on to carry out a brief but intense campaign to ban the use of AC or to limit the allowable voltage for safety purposes. As part of this campaign, Edison's employees publicly electrocuted animals to demonstrate the dangers of AC; alternating electric currents are slightly more dangerous in that frequencies near 60 Hz have a markedly greater potential for inducing fatal "cardiac fibrillation" than do direct currents. On one of the more notable occasions, in 1903, Edison's workers electrocuted Topsy the elephant at Luna Park, near Coney Island, after she had killed several men and her owners wanted her put to death. His company filmed the electrocution.
AC replaced DC in most instances of generation and power distribution, enormously extending the range and improving the efficiency of power distribution. Though widespread use of DC ultimately lost favor for distribution, it exists today primarily in long-distance high-voltage direct current (HVDC) transmission systems. Low voltage DC distribution continued to be used in high-density downtown areas for many years but was eventually replaced by AC low-voltage network distribution in many of them. DC had the advantage that large battery banks could maintain continuous power through brief interruptions of the electric supply from generators and the transmission system. Utilities such as Commonwealth Edison in Chicago had rotary converters or motor-generator sets, which could change DC to AC and AC to various frequencies in the early to mid-20th century. Utilities supplied rectifiers to convert the low voltage AC to DC for such DC loads as elevators, fans and pumps. There were still 1,600 DC customers in downtown New York City as of 2005, and service was finally discontinued only on November 14, 2007. Most subway systems still are powered by direct current.
Edison is credited with designing and producing the first commercially available fluoroscope, a machine that uses X-rays to take radiographs. Until Edison discovered that calcium tungstate fluoroscopy screens produced brighter images than the barium platinocyanide screens originally used by Wilhelm Röntgen, the technology was capable of producing only very faint images. The fundamental design of Edison's fluoroscope is still in use today, despite the fact that Edison himself abandoned the project after nearly losing his own eyesight and seriously injuring his assistant, Clarence Dally. Dally had made himself an enthusiastic human guinea pig for the fluoroscopy project and in the process been exposed to a poisonous dose of radiation. He later died of injuries related to the exposure. In 1903, a shaken Edison said "Don't talk to me about X-rays, I am afraid of them."
Frank J. Sprague, a competent mathematician and former naval officer, was recruited by Edward H. Johnson and joined the Edison organization in 1883. One of Sprague's significant contributions to the Edison Laboratory at Menlo Park was to expand Edison's mathematical methods. Despite the common belief that Edison did not use mathematics, analysis of his notebooks reveal that he was an astute user of mathematical analysis conducted by his assistants such as Francis Robbins Upton, for example, determining the critical parameters of his electric lighting system including lamp resistance by a sophisticated analysis of Ohm's Law, Joule's Law and economics.
Another of Edison's assistants was Nikola Tesla. Tesla claimed that Edison promised him $50,000 if he succeeded in making improvements to his DC generation plants. Several months later, when Tesla had finished the work and asked to be paid, he said that Edison replied, "When you become a full-fledged American you will appreciate an American joke." Tesla immediately resigned. With Tesla's salary of $18 per week, the payment would have amounted to over 53 years' pay and the amount was equal to the initial capital of the company. Tesla resigned when he was refused a raise to $25 per week. Although Tesla accepted an Edison Medal later in life, this and other negative series of events concerning Edison remained with Tesla. The day after Edison died, the New York Times contained extensive coverage of Edison's life, with the only negative opinion coming from Tesla who was quoted as saying:
He had no hobby, cared for no sort of amusement of any kind and lived in utter disregard of the most elementary rules of hygiene. [...] His method was inefficient in the extreme, for an immense ground had to be covered to get anything at all unless blind chance intervened and, at first, I was almost a sorry witness of his doings, knowing that just a little theory and calculation would have saved him 90% of the labour. But he had a veritable contempt for book learning and mathematical knowledge, trusting himself entirely to his inventor's instinct and practical American sense.—Nikola Tesla
One of Edison's famous quotations regarding his attempts to make the light globe suggest that perhaps Tesla was right about Edison's methods of working: "If I find 10,000 ways something won't work, I haven't failed. I am not discouraged, because every wrong attempt discarded is another step forward."
When Edison was a very old man and close to death, he said, in looking back, that the biggest mistake he had made was that he never respected Tesla or his work.
There were 28 men recognized as Edison Pioneers.
The key to Edison's fortunes was telegraphy. With knowledge gained from years of working as a telegraph operator, he learned the basics of electricity. This allowed him to make his early fortune with the stock ticker, the first electricity-based broadcast system. Edison patented the sound recording and reproducing phonograph in 1878. Edison was also granted a patent for the motion picture camera or "Kinetograph". He did the electromechanical design, while his employee W.K.L. Dickson, a photographer, worked on the photographic and optical development. Much of the credit for the invention belongs to Dickson. In 1891, Thomas Edison built a Kinetoscope, or peep-hole viewer. This device was installed in penny arcades, where people could watch short, simple films. The kinetograph and kinetoscope were both first publicly exhibited May 20, 1891.
On August 9, 1892, Edison received a patent for a two-way telegraph. In April 1896, Thomas Armat's Vitascope, manufactured by the Edison factory and marketed in Edison's name, was used to project motion pictures in public screenings in New York City. Later he exhibited motion pictures with voice soundtrack on cylinder recordings, mechanically synchronized with the film.
Officially the kinetoscope entered Europe when the rich American Businessman Irving T. Bush (1869–1948) bought from the Continental Commerce Company of Franck Z. Maguire and Joseph D. Bachus a dozen machines. Bush placed from October 17, 1894, the first kinetoscopes in London. At the same time the French company Kinétoscope Edison Michel et Alexis Werner bought these machines for the market in France. In the last three months of 1894 The Continental Commerce Company sold hundreds of kinetoscopes in Europe (i.e. the Netherlands and Italy). In Germany and in Austria-Hungary the kinetoscope was introduced by the Deutsche-österreichische-Edison-Kinetoscop Gesellschaft, founded by the Ludwig Stollwerck of the Schokoladen-Süsswarenfabrik Stollwerck & Co of Cologne. The first kinetoscopes arrived in Belgium at the Fairs in early 1895. The Edison's Kinétoscope Français, a Belgian company, was founded in Brussels on January 15, 1895, with the rights to sell the kinetoscopes in Monaco, France and the French colonies. The main investors in this company were Belgian industrialists. On May 14, 1895, the Edison's Kinétoscope Belge was founded in Brussels. The businessman Ladislas-Victor Lewitzki, living in London but active in Belgium and France, took the initiative in starting this business. He had contacts with Leon Gaumont and the American Mutoscope and Biograph Co. In 1898 he also became a shareholder of the Biograph and Mutoscope Company for France.
In 1901, he visited the Sudbury area in Ontario, Canada, as a mining prospector, and is credited with the original discovery of the Falconbridge ore body. His attempts to actually mine the ore body were not successful, however, and he abandoned his mining claim in 1903. A street in Falconbridge, as well as the Edison Building, which served as the head office of Falconbridge Mines, are named for him.
In 1902, agents of Thomas Edison bribed a theater owner in London for a copy of A Trip to the Moon by Georges Méliès. Edison then made hundreds of copies and showed them in New York City. Méliès received no compensation. He was counting on taking the film to the US and recapture its huge cost by showing it throughout the country when he realized it had already been shown there by Edison. This effectively bankrupted Méliès. Other exhibitors similarly routinely copied and exhibited each others films. To better protect the copyrights on his films, Edison deposited prints of them on long strips of photographic paper with the U.S. copyright office. Many of these paper prints survived longer and in better condition than the actual films of that era.
Edison's favorite movie was The Birth of a Nation. He thought that talkies had "spoiled everything" for him. "There isn't any good acting on the screen. They concentrate on the voice now and have forgotten how to act. I can sense it more than you because I am deaf." His favorite stars were Mary Pickford and Clara Bow.
In 1908, Edison started the Motion Picture Patents Company, which was a conglomerate of nine major film studios (commonly known as the Edison Trust). Thomas Edison was the first honorary fellow of the Acoustical Society of America, which was founded in 1929.
Edison moved from Menlo Park after the death of Mary Stilwell and purchased a home known as "Glenmont" in 1886 as a wedding gift for Mina in Llewellyn Park in West Orange, New Jersey. In 1885, Thomas Edison bought property in Fort Myers, Florida, and built what was later called Seminole Lodge as a winter retreat. Edison and his wife Mina spent many winters in Fort Myers where they recreated and Edison tried to find a domestic source of natural rubber.
Henry Ford, the automobile magnate, later lived a few hundred feet away from Edison at his winter retreat in Fort Myers, Florida. Edison even contributed technology to the automobile. They were friends until Edison's death.
In 1928, Edison joined the Fort Myers Civitan Club. He believed strongly in the organization, writing that "The Civitan Club is doing things —big things— for the community, state, and nation, and I certainly consider it an honor to be numbered in its ranks." He was an active member in the club until his death, sometimes bringing Henry Ford to the club's meetings.
Edison was active in business right up to the end. Just months before his death in 1931, the Lackawanna Railroad implemented electric trains in suburban service from Hoboken to Gladstone, Montclair and Dover in New Jersey. Transmission was by means of an overhead catenary system, with the entire project under Edison's guidance. To the surprise of many, he was at the throttle of the very first MU (Multiple-Unit) train to depart Lackawanna Terminal in Hoboken, driving the train all the way to Dover. As another tribute to his lasting legacy, the same fleet of cars Edison deployed on the Lackawanna in 1931 served commuters until their retirement in 1984, when some of them were purchased by the Berkshire Scenic Railway Museum in Lenox, Massachusetts. A special plaque commemorating the joint achievement of both the railway and Edison can be seen today in the waiting room of Lackawanna Terminal in Hoboken, presently operated by New Jersey Transit.
Edison was said to have been influenced by a popular fad diet in his last few years; "the only liquid he consumed was a pint of milk every three hours". He is reported to have believed this diet would restore his health. However, this tale is doubtful. In 1930, the year before Edison died, Mina said in an interview about him that "Correct eating is one of his greatest hobbies." She also said that during one of his periodic "great scientific adventures", Edison would be up at 7:00, have breakfast at 8:00, and be rarely home for lunch or dinner, implying that he continued to have all three.
Edison became the owner of his Milan, Ohio, birthplace in 1906. On his last visit, in 1923, he was shocked to find his old home still lit by lamps and candles.
Thomas Edison died of complications of diabetes on October 18, 1931, in his home, "Glenmont" in Llewellyn Park in West Orange, New Jersey, which he had purchased in 1886 as a wedding gift for Mina. He is buried behind the home.
Edison's last breath is reportedly contained in a test tube at the Henry Ford Museum. Ford reportedly convinced Charles Edison to seal a test tube of air in the inventor's room shortly after his death, as a memento. A plaster death mask was also made.
Mina died in 1947.
Historian Paul Israel has characterized Edison as a "freethinker". Edison was heavily influenced by Thomas Paine's The Age of Reason. Edison defended Paine's "scientific deism", saying, "He has been called an atheist, but atheist he was not. Paine believed in a supreme intelligence, as representing the idea which other men often express by the name of deity." In an October 2, 1910, interview in the New York Times Magazine, Edison stated:
Nature is what we know. We do not know the gods of religions. And nature is not kind, or merciful, or loving. If God made me — the fabled God of the three qualities of which I spoke: mercy, kindness, love — He also made the fish I catch and eat. And where do His mercy, kindness, and love for that fish come in? No; nature made us — nature did it all — not the gods of the religions.
Edison was called an atheist for those remarks, and although he did not allow himself to be drawn into the controversy publicly, he clarified himself in a private letter: "You have misunderstood the whole article, because you jumped to the conclusion that it denies the existence of God. There is no such denial, what you call God I call Nature, the Supreme intelligence that rules matter. All the article states is that it is doubtful in my opinion if our intelligence or soul or whatever one may call it lives hereafter as an entity or disperses back again from whence it came, scattered amongst the cells of which we are made."
Nonviolence was key to Edison's moral views, and when asked to serve as a naval consultant for World War I, he specified he would work only on defensive weapons and later noted, "I am proud of the fact that I never invented weapons to kill." Edison's philosophy of nonviolence extended to animals as well, about which he stated: "Nonviolence leads to the highest ethics, which is the goal of all evolution. Until we stop harming all other living beings, we are still savages." However, he is also notorious for having electrocuted a number of dogs in 1888, both by direct and alternating current, in an attempt to argue that the former (which he had a vested business interest in promoting) was safer than the latter (favored by his rival George Westinghouse). Edison's success in promoting direct current as less lethal also led to alternating current being used in the electric chair adopted by New York in 1889 as a supposedly humane execution method; because Westinghouse was angered by the decision, he funded Eighth Amendment-based appeals for inmates set to die in the electric chair, ultimately resulting in Edison providing the generators which powered early electrocutions and testifying successfully on behalf of the state that electrocution was a painless method of execution.
Several places have been named after Edison, most notably the town of Edison, New Jersey. Thomas Edison State College, a nationally known college for adult learners, is in Trenton, New Jersey. Two community colleges are named for him: Edison State College in Fort Myers, Florida, and Edison Community College in Piqua, Ohio. There are numerous high schools named after Edison; see Edison High School.
The City Hotel, in Sunbury, Pennsylvania, was the first building to be lit with Edison's three-wire system. The hotel was re-named The Hotel Edison, and retains that name today.
Three bridges around the United States have been named in his honor (see Edison Bridge).
In West Orange, New Jersey, the 13.5 acre (5.5 ha) Glenmont estate is maintained and operated by the National Park Service as the Edison National Historic Site. The Thomas Alva Edison Memorial Tower and Museum is in the town of Edison, New Jersey. In Beaumont, Texas, there is an Edison Museum, though Edison never visited there. The Port Huron Museum, in Port Huron, Michigan, restored the original depot that Thomas Edison worked out of as a young newsbutcher. The depot has been named the Thomas Edison Depot Museum. The town has many Edison historical landmarks, including the graves of Edison's parents, and a monument along the St. Clair River. Edison's influence can be seen throughout this city of 32,000. In Detroit, the Edison Memorial Fountain in Grand Circus Park was created to honor his achievements. The limestone fountain was dedicated October 21, 1929, the fiftieth anniversary of the creation of the lightbulb. On the same night, The Edison Institute was dedicated in nearby Dearborn.
In early 2010, Edison was proposed by the Ohio Historical Society as a finalist in a statewide vote for inclusion in Statuary Hall at the United States Capitol.
The Edison Medal was created on February 11, 1904, by a group of Edison's friends and associates. Four years later the American Institute of Electrical Engineers (AIEE), later IEEE, entered into an agreement with the group to present the medal as its highest award. The first medal was presented in 1909 to Elihu Thomson and, in a twist of fate, was awarded to Nikola Tesla in 1917. It is the oldest award in the area of electrical and electronics engineering, and is presented annually "for a career of meritorious achievement in electrical science, electrical engineering or the electrical arts."
In the Netherlands, the major music awards are named the Edison Award after him.
The American Society of Mechanical Engineers concedes the Thomas A. Edison Patent Award to individual patents since 2000.
The President of the Third French Republic, Jules Grévy, on the recommendation of his Minister of Foreign Affairs Jules Barthélemy-Saint-Hilaire and with the presentations of the Minister of Posts and Telegraphs Louis Cochery, designated Edison with the distinction of an 'Officer of the Legion of Honour' (Légion d'honneur) by decree on November 10, 1881;
In 1983, the United States Congress, pursuant to Senate Joint Resolution 140 (Public Law 97—198), designated February 11, Edison's birthday, as National Inventor's Day.
In 1887, Edison won the Matteucci Medal. In 1890, he was elected a member of the Royal Swedish Academy of Sciences.
In 1889, Edison was awarded the John Scott Medal.
In 1899, Edison was awarded the Edward Longstreth Medal.
Edison was awarded Franklin Medal of The Franklin Institute in 1915 for discoveries contributing to the foundation of industries and the well-being of the human race.
Edison was ranked thirty-fifth on Michael H. Hart's 1978 book The 100, a list of the most influential figures in history. Life magazine (USA), in a special double issue in 1997, placed Edison first in the list of the "100 Most Important People in the Last 1000 Years", noting that the light bulb he promoted "lit up the world". In the 2005 television series The Greatest American, he was voted by viewers as the fifteenth-greatest.
In 2008, Edison was inducted in the New Jersey Hall of Fame.
The United States Navy named the USS Edison (DD-439), a Gleaves class destroyer, in his honor in 1940. The ship was decommissioned a few months after the end of World War II. In 1962, the Navy commissioned USS Thomas A. Edison (SSBN-610), a fleet ballistic missile nuclear-powered submarine. Decommissioned on December 1, 1983, Thomas A. Edison was stricken from the Naval Vessel Register on April 30, 1986. She went through the Navy's Nuclear Powered Ship and Submarine Recycling Program at Bremerton, Washington, beginning on October 1, 1996. When she finished the program on December 1, 1997, she ceased to exist as a c
A parabolic aluminized reflector lamp (also PAR light, PAR can, or simply PAR) is a type of electric lamp that is widely used in commercial, residential, and transportation illumination. Usage includes locomotive headlamps, aircraft landing lights, and residential and commercial recessed lights ("cans" in the United States). They are identical in principle to sealed beam automobile headlights.
This article covers only their use in stage lighting. The lamps and their fixtures are widely used in theatre, concerts and motion picture production when a substantial amount of flat lighting is required for a scene.
They are frequently used in patterns of multiple lights such as 3 by 3 (known as a "nine light") when large areas are to be lit.
In situations where sunlight or other specular light is available, a white foam reflector is often used to accomplish the same effect as a PAR array.
PAR cans are being replaced in some applications by LED PAR cans, which use less electric power and produce a wide array of saturated colors without the use of color filters, when white light is not needed.
PAR lights possess a lens and reflector that are integral parts of the lamp, the position of which cannot be altered relative to the filament. A notable exception is ETC's Source Four PAR, which uses the same halogen lamp as their Source Four ERS. In this case, the lens is a separate piece from the lamp. The relative position of lamp and lens remains unalterable.
In PAR 64s, Raylite reflectors and two pin base lamps are often used as a cheaper alternative as the lamp is replaced but the reflector remains. Lamps such as the 500 watt A1/244 can be as much as half the price of the sealed beam units. Par 64's also often run at 120 V, in two-pair series channels, with a "y" Splitter at the dimmer. Narrow, medium and wide Raylite refectors are quite readily available. The two-blade (pin) Mogul lamp connector need not be replaced — this is integral to the Raylite reflector, although some Raylite reflectors have "tails" which then require connection to the mains flex with the use of a ceramic connector block (ideally fixed to the can's body).
The sealed beam lamp produces an intense oval pool of light with unfocused edges. The only focus adjustment is a knob that allows the lamp/lens unit to be rotated within its casing, thus changing the orientation of the oval. With some models this control is via the mogul ceramic connector which connects directly to the Mogul prongs of the lamp. With the SourceFour PAR, the interchangeable lens is what is rotated. Therefore, the diameter of the light spot is defined by the aluminium reflector, and cannot be adjusted without changing the lamp. The type of lamp includes extra-wide flood (XWFL), wide flood (WFL), medium flood (MFL), narrow spot (NSP), and very narrow spot (VNSP).
These types of instruments come in varying diameters, the most common being designated PAR56 and PAR64. The number indicates the diameter of the housing in eighths of an inch (so a PAR64 is eight inches (~20 cm) in diameter).
PAR lights are often used in theatrical or live music shows. Commonly they are used to generate colours by fitting them with colored sheets called gels. The cans are arranged into rows of different colours and identical rows placed on different sides of the stage. Due to their affordability, they are ideal for colour washes in several different colours. However, because of the lack of control over the beam diameter, shape and sharpness, PARs are rarely used as front of house lights other than for front washes but can be used for special effect lighting such as lighting from directly above or from extreme angles as well as general wash lights overhead/above stage. If used cleverly, par cans can provide low budget productions with good effects.
Nominal lamp bell diameter in inches is found by dividing the PAR size by 8. For example, a PAR30 lamp is approximately 3.75 inches in diameter.
Note: PAR16 is also known as a "birdie" in theatre, as it is "below par", an oblique reference to a term used in the game of golf.
Depending the parabolic reflector geometry and placement of the filament within the paraboloid, PAR lamps can achieve a wide range of beam widths, from narrow spot to wide flood. For lighting effects even wider than wide flood can provide, supplemental reflectors or lenses can be used. The following suffixes are commonly used with PAR lamps to indicate their beam width:
|Very Narrow Spot||CP60|
|Medium Flood 1||CP62|
Each lamp type is available in 110 V or 220 V rating, depending on the common mains voltage for a locale, except ACL PAR, whose light beam is more compact and nominal operating voltage is 28 V. ACL PAR is a type of projector primarily used in aviation, before being used on stage for light path effects.
Raylite reflectors can be added to PAR64 and PAR56 lamp housings to achieve a narrow spot effect. A conventional quartz halogen lamp is used in place of the reflector lamp. A spider or bulb shield may optionally be added, which enhances the parallel nature of the beam and makes it more visible when used with smoke or fog effects.
PARs are found commonly with either black finish or polished (silver). PARs can occasionally be found in white.
The Source Four PAR and similar units create light with a similar quality to that of a PAR can, but have lenses separate from the lamp.
An LED version of the PAR is made by some manufacturers.
LED PAR cans usually are based on an RGB color model.
PARbars are PARs that are permanently affixed to and circuited through an aluminum pipe. Four PARs on a bar are called a 4-bar. 6 PARs are called 6-bars.
HMI PARs produce light with a color temperature equivalent to that of sunlight.
Intelligent, moving PARs allow for the ability to pan and tilt the instruments through a lighting control console.
Black light fluorescent tubes. The purple glow of a black light is not the UV light itself, which is invisible, but visible light which escapes being filtered out by the filter material in the glass envelope.
A black light, also referred to as a UV light (Ultra Violet Light), is a lamp that emits electromagnetic radiation almost exclusively in the soft near ultraviolet range. Only a very small fraction of visible radiation passes through the filtering material, with wavelengths no longer than 400-410 nm, and as a result, the human eye detects its color as deep blue and violet. Wood's glass is an example of filtering material which is transparent to ultraviolet wavelengths between 320 and 400 nm.
Black light sources may be made from specially designed fluorescent lamps, mercury vapor lamps, light-emitting diodes, or incandescent lamps. In most black lights either the glass envelope of the lamp itself or the lamp enclosure has an optical filter designed to reduce the emission of visible light and pass desired parts of the ultraviolet spectrum. In medicine, forensics, and some other scientific fields, such a light source is referred to as a Wood's lamp (named after Robert Williams Wood).
Black light sources have many uses. They may be employed for decorative and artistic lighting effects, for diagnostic and therapeutic uses in medicine, for the eradication of microorganisms, for the observation or detection of substances tagged with other substances that exhibit a fluorescent effect, for the curing of plastic resins and for attracting insects. Strong sources of long-wave ultraviolet light are used in tanning beds. Black light lamps are used for the detection of counterfeit money. Most artificial ultraviolet sources are low power. Powerful ultraviolet sources present a hazard to eyes and skin; apparatus using these sources requires personal protective equipment.
A black light, or Wood's light, is a lamp that emits long wave UV radiation (generally with a wavelength above 300 nm) and very little visible light. They are sometimes referred to as a "UV light". Fluorescent black lights are typically made in the same fashion as normal fluorescent lights except that only one phosphor is used, and the clear glass envelope of the bulb may be replaced by a deep-bluish-purple glass called Wood's glass, a nickel-oxide–doped glass, which blocks almost all visible light between 400 and 700 nanometres. The color of such lamps is often referred to in the trade as "blacklight blue" or "BLB." This is to distinguish these lamps from "bug zapper" blacklight ("BL") lamps that do not have the blue Wood's glass. The phosphor typically used for a near 368 to 371 nanometre emission peak is either europium-doped strontium fluoroborate (SrB4O7F:Eu2+) or europium-doped strontium borate (SrB4O7:Eu2+) while the phosphor used to produce a peak around 350 to 353 nanometres is lead-doped barium silicate (BaSi2O5:Pb+). "Blacklight Blue" lamps peak at 365 nm.
A black light may also be formed by simply using Wood's glass instead of clear glass as the envelope for a common incandescent bulb. This was the method used to create the very first black light sources. Though it remains a cheaper alternative to the fluorescent method, it is exceptionally inefficient at producing UV light (less than 0.1% of the input power), owing to the black body nature of the incandescent light source. Incandescent UV bulbs, due to their inefficiency, may also become dangerously hot during use. More rarely still, high-power (hundreds of watts) mercury-vapor black lights that use a UV-emitting phosphor and an envelope of Wood's glass can be found. These lamps are used mainly for theatrical and concert displays, and also become very hot during normal use.
Some UV fluorescent bulbs specifically designed to attract insects use the same near-UV emitting phosphor as normal blacklights, but use plain glass instead of the more expensive Wood's glass. Plain glass blocks less of the visible mercury emission spectrum, making them appear light-blue to the naked eye. These lamps are referred to as "blacklight" or "BL" in most lighting catalogs.
Black light fluorescent tubes are typically made in the same way as normal fluorescent lights except that only one phosphor is used and the normally clear glass envelope of the bulb may be replaced by a deep-bluish-purple glass called Wood's glass. In practice, partly due to cost but mainly because Wood's glass does not make a satisfactory material for lamp manufacturing, the lamp will be made from normal glass with a relatively thin coating of a UV filtering material applied to the exterior. The color of such lamps is often referred to in the trade as "blacklight blue" or "BLB". This is to distinguish these lamps from "bug zapper" blacklight ("BL") lamps that do not have the filter material.
The phosphor typically used for a near 368 to 371 nanometer UV emission peak is either europium-doped strontium fluoroborate (SrB4O7F:Eu2+) or europium-doped strontium borate (SrB4O7:Eu2+) while the phosphor used to produce a peak at around 350–353 nm is lead-doped barium silicate (BaSi2O5:Pb+). "Blacklight Blue" lamps peak at 365 nm.
Manufacturers use different numbering systems for black light, UVA, UVB and Actinic tubes. Philips uses one system which is becoming outdated (2010), while the (German) Osram system is becoming dominant outside North America. The following table lists the tubes generating blue, UVA and UVB, in order of decreasing wavelength of the most intense peak. Approximate phosphor compositions, major manufacturer's type numbers and some uses are given as an overview of the types available. "Peak" position is approximated to the nearest 10 nm. "Width" is the measure between points on the shoulders of the peak that represent 50% intensity.
|Phosphor||Peak, nm||Width, nm||Philips Suffix.||Osram Suffix.||U.S. Type||Uses|
|SrB4O7, Eu||370||20||/08||/73||("BLB")||forensics, night clubs|
|SrB4O7, Eu||370||20||-||/78||("BL")||insect attraction, polymerization, psoriasis, suntanning|
|BaSi2O5, Pb||350||40||/09||/79||"BL"||insect attraction, suntanning lounges|
|BaSi2O5, Pb||350||40||/08||-||"BLB"||dermatology, forensics, night clubs|
|SrAl11O18, Ce||340||30||-||-||-||photochemical uses|
|MgSrAl10O17, Ce||310||40||-||-||-||medical applications, polymerization|
Wood's glass tubes manufactured by Osram use a fairly narrow-band emitting phosphor, europium activated strontium pyroborate with a peak at about 370 nm, whereas North American and Philips Wood's glass tubes use lead-activated calcium metasilicate that emits a wider band with a shorter wavelength peak at about 350 nm. These two types seem to be the most commonly used. Different manufacturers offer either one or the other and sometimes both.
Some UV fluorescent bulbs are designed for use, particularly in kitchens, to attract insects for electrocution in bug zappers. These use the same near-UV emitting phosphor as normal black lights, but use plain glass instead of the more expensive Wood's glass or filter-coated glass. Plain glass blocks out less of the visible mercury emission spectrum, making them appear light blue-violet to the naked eye. These lamps are referred to as "blacklight" or "BL" in most North American lighting catalogs.
European equivalents are the Philips TL-XXW/09, emitting a peak at 350 nm, and the Osram LXXW/78, emitting a peak at 371 nm, among others.
A black light may also be formed by simply using Wood's glass as the envelope for a common incandescent bulb. This was the method that was used to create the very first black light sources. Although it remains a cheaper alternative to fluorescent tubes, it is exceptionally inefficient at producing UV light since most of the light emitted by the filament is visible light which must be blocked. Due to its black body spectrum, an incandescent light radiates less than 0.1% of its energy as UV light. Incandescent UV bulbs, due to the necessary absorption of the visible light, become very hot during use. This heat is, in fact, encouraged in such bulbs, since a hotter filament increases the proportion of UVA in the black-body radiation emitted. This high running-temperature drastically reduces the life of the lamp, however, from a typical 1000 hours to around 100 hours.
High power mercury vapor black lamps have a normal range of power input of between 100 and 1000 Watts. These do not use phosphors, but rely on the intensified and slightly broadened 350–375 nm spectral line of mercury from high pressure discharge at between 5 and 10 standard atmospheres (500 and 1,000 kPa), depending upon the specific type. These lamps use envelopes of Wood's glass to block out all the visible lines of Mercury and the short wavelength UVC resonance lines, which are harmful. A few other spectral lines, falling within the pass band of the Wood's glass between 300 and 400 nm, contribute to the output.
These lamps are used mainly for theatrical purposes and concert displays. They are far more effective UVA producers per unit of power consumption than are incandescent lamps.
Ultraviolet light can be generated by some light-emitting diodes, but wavelengths below 380 nm are uncommon and the emission peaks are broad, so only the very lowest energy UV photons are emitted, within predominantly visible light.
Although black lights produce light in the UV range, their spectrum is mostly confined to the longwave UVA region, that is, UV radiation nearest in wavelength to visible light, with low frequency and therefore relatively low energy. While low, There is still some power of a conventional black light in the UVB range.  UVA is the safest of the three spectra of UV light, although high exposure to UVA has been linked to the development of skin cancer in humans. The relatively low energy of UVA light does not cause sunburn. UVA is capable of causing damage to collagen fibers, however, so it does have the potential to accelerate skin aging and cause wrinkles. UVA can also destroy vitamin A in the skin.
UVA light has been shown to cause DNA damage, but not directly, like UVB and UVC. Due to its longer wavelength, it is absorbed less and reaches deeper into skin layers, where it produces reactive chemical intermediates such as hydroxyl and oxygen radicals, which in turn can damage DNA and result in a risk of melanoma. The weak output of black lights, however, is not considered sufficient to cause DNA damage or cellular mutations in the way that direct summer sunlight can, although there are reports that overexposure to the type of UV radiation used for creating artificial suntans on sunbeds can cause DNA damage, photoaging (damage to the skin from prolonged exposure to sunlight), toughening of the skin, suppression of the immune system, cataract formation and skin cancer.
Ultraviolet radiation is invisible to the human eye, but illuminating certain materials with UV radiation causes the emission of visible wavelengths that give rise to an effect of fluorescence or phosphorescence.
Black light is commonly used to authenticate oil paintings, antiques and banknotes. Black lights can be used to differentiate real currency from counterfeit notes because, in many countries, legal banknotes have fluorescent symbols on them that only show under a black light. In addition, the paper used for printing money does not contain any of the brightening agents which cause commercially available papers to fluoresce under black light. Both of these features make illegal notes easier to detect and more difficult to successfully counterfeit. The same security features can be applied to identification cards.
Other security applications include the use of pens containing a fluorescent ink, generally with a soft tip, than can be used to "invisibly" mark items. If the objects that are so marked are subsequently stolen, a black light can be used to search for these security markings. At some theme parks and at other, day-long (or night-long) events, a fluorescent mark is rubber stamped onto the wrist of a guest who can then exercise the option of leaving and being able to return again without paying another admission fee.
In medicine, the Wood's lamp is used to check for the characteristic fluorescence of certain dermatophytic fungi such as species of Microsporan which emit a yellow glow, or corynebacterium which have a red to orange color when viewed under a Wood's lamp. Such light is also used to detect the presence and extent of disorders that cause a loss of pigmentation, such as vitiligo. It can also be used to diagnose ringworm, fungal infections, corneal scratches, foreign bodies in the eye, blocked tear ducts, acne, erythrasma, tinea versicolor, microsporum canis, scabies, alopecia, porphyria, bacterial infections, and many other skin conditions. Fluorescent materials are also very widely used in numerous applications in molecular biology, often as "tags" which bind themselves to a substance of interest (for example, DNA), so allowing their visualization. Black light can also be used to see animal excreta such as urine and vomit that is not always visible to the naked eye.
Black light is used extensively in non-destructive testing. Fluorescing fluids are applied to metal structures and illuminated with a black light which allows cracks and other weaknesses in the material to be easily detected. It is also used to illuminate pictures painted with fluorescent colors, particularly on black velvet, which intensifies the illusion of self-illumination. The use of such materials, often in the form of tiles viewed in a sensory room under UV light, is common in the United Kingdom for the education of students with profound and multiple learning difficulties. Such fluorescence from certain textile fibers, especially those bearing optical brightener residues, can also be used for recreational effect, as seen, for example, in the opening credits of the James Bond film A View to a Kill. Black light puppetry is also performed in a black light theater.
One of the innovations for night and all-weather flying used by the US, UK and Germany during World War II was the use of UV interior lighting to illuminate the instrument panel, giving a safer alternative to the radium-painted instrument faces and pointers, and an intensity that could be varied easily and without visible illumination that would give away an aircraft's position. This went so far as to include the printing of charts that were marked in UV-fluorescent inks, and the provision of UV-visible pencils and slide rules such as the E6B.
A grow light or plant light is an artificial light source, generally an electric light, designed to stimulate plant growth by emitting an electromagnetic spectrum appropriate for photosynthesis. Grow lights are used in applications where there is either no naturally occurring light, or where supplemental light is required. For example, in the winter months when the available hours of daylight may be insufficient for the desired plant growth, grow lights are used to extend the amount of time the plants receive light.
Grow lights either attempt to provide a light spectrum similar to that from the sun, or to provide a spectrum that is more tailored to the needs of the plants being cultivated. Outdoor conditions are mimicked with varying colour temperatures and spectral outputs from the grow light, as well as varying the lumen output (intensity) of the lamps. Depending on the type of plant being cultivated, the stage of cultivation (E.G.: the germination/vegetative phase or the flowering/fruiting phase), and the photoperiod required by the plants, specific ranges of spectrum, luminous efficacy and colour temperature are desirable for use with specific plants and time periods.
Grow lights are used for indoor gardening, plant propagation and food production, including indoor hydroponics and aquatic plants. Although most grow lights are used on an industrial level, they can also be used in households.
According to the inverse square law, the intensity of light radiating from a point source (in this case a bulb) that reaches a surface is inversely proportional to the square of the surface's distance from the source (if an object is twice as far away, it receives only a quarter the light) which is a serious hurdle for indoor growers, and many techniques are employed to use light as efficiently as possible. Reflectors are thus often used in the lights to maximize light efficiency. Plants or lights are moved as close together as possible so that they receive equal lighting and that all light coming from the lights falls on the plants rather than on the surrounding area.
Often, the distance between light and plant is as far as 60 cm (24 in) (with incandescent lights) up to 10 cm (4 in) (with other lights as compact, large and high-output fluorescent lights). Many home gardeners cover the walls of their grow-room with a reflective material, or alternatively, white paint to maximize efficiency.
A range of bulb types can be used as grow lights, such as incandescents, fluorescent lights, high-intensity discharge lights, and LEDs. Today, the most widely used lights for professional use are HIDs and fluorescents. Indoor flower and vegetable growers typically use high pressure sodium (HPS/SON) and metal halide (MH) HID lights, but fluorescents are replacing metal halides due to their efficiency and economy.
Metal halide lights are used for the first (or vegetative) phase of growth as they have a bluish light.
Blue spectrum light may trigger a greater vegetative response in plants.
High pressure sodium lights are used for the second (or reproductive) phase of growth as they have a reddish light.
Red spectrum light may trigger a greater flowering response in plants. If high pressure sodium lights are used for the vegetative phase, plants grow slightly more quickly, but will have longer internodes, and may be longer overall.
Also, MH bulbs with added reddish spectrum and HPS bulbs with added bluish spectrum are also available for fuller spectrum and added flexibility during both vegetative and flowering phases.
Natural daylight has a high color temperature (approx. 6000 K). Visible light color varies according to the weather, and angle of the Sun, and specific quantities (measured in Lumens) of light stimulate photosynthesis. Distance from the sun has little effect on seasonal changes in the quality and quantity of light and the resulting plant behavior during those seasons. The Earth tilts on its axis as it revolves around the sun. During the summer we get nearly direct sunlight and during the winter we get sunlight at a 23.44 degree angle to the equator. This small tilt of the Earth's axis changes the effective thickness of the atmosphere with respect to the distance sunlight has to travel to reach our particular area on Earth. The color spectrum of light that the sun sends us does not change, only the quantity [more during the summer and less on winter] and quality of overall light reaching us. The color rendering index allows comparison of how closely the light matches the natural color of regular sunlight.
Different stages of plant growth require different spectra. The initial vegetative stage requires blue spectrum of light, whereas the later "flowering" stage is usually done with red–orange spectra. Light bulbs can be manufactured with a specific spectrum range or can be full spectrum, such as the Sylvania GRO-LUX.
The light is used in conjunction with a reflector to control and intensify the light emissions and will include an electrical ballast to convert mains AC to DC, setting the voltage and amps appropriately to power the light.
The following table lists luminous efficacy of a source and efficiency for various light sources:
luminous efficacy (lm/W)
|Incandescent||100–200 W tungsten incandescent (230 V)||13.8–15.2||2.0–2.2%|
|100–200–500 W tungsten glass halogen (230 V)||16.7–17.6–19.8||2.4–2.6–2.9%|
|5–40–100 W tungsten incandescent (120 V)||5–12.6–17.5||0.7–1.8–2.6%|
|2.6 W tungsten glass halogen (5.2 V)||19.2||2.8%|
|tungsten quartz halogen (12–24 V)||24||3.5%|
|photographic and projection lights||35||5.1%|
|Light-emitting diode||white LED (raw, without power supply)||4.5–150 ||0.66–22.0%|
|4.1 W LED screw base light (120 V)||58.5–82.9||8.6–12.1%|
|6.9 W LED screw base light (120 V)||55.1–81.9||8.1–12.0%|
|7 W LED PAR20 (120 V)||28.6||4.2%|
|8.7 W LED screw base light (120 V)||69.0–93.1||10.1–13.6%|
|Arc light||xenon arc light||30–50||4.4–7.3%|
|mercury-xenon arc light||50–55||7.3–8.0%|
|Fluorescent||T12 tube with magnetic ballast||60||9%|
|9–32 W compact fluorescent||46–75||8–11.45%|
|T8 tube with electronic ballast||80–100||12–15%|
|PL-S 11W U-tube with traditional ballast||82||12%|
|Spiral tube with electronic ballast||114-124.3||15–18%|
|Gas discharge||1400 W sulfur light||100||15%|
|metal halide light||65–115||9.5–17%|
|high pressure sodium light||85–150||12–22%|
|low pressure sodium light||100–200||15–29%|
|Cathodoluminescence||electron stimulated luminescence||30||5%|
|Ideal sources||Truncated 5800 K blackbody||251||37%|
|Green light at 555 nm (maximum possible luminous efficacy)||683.002||100%|
Incandescent grow lights have a red-yellowish tone and low color temperature (approx. 2700 K). They are used to highlight indoor plant groupings and not as a true plant 'growing' light (although they may be labeled as such). Incandescent growing lights have an average life span of 750 hours. In addition, they are less energy efficient than fluorescent or high-intensity discharge lights, converting much of the electricity consumed into heat (rather than light).
Today, fluorescent lights are available in any desired color temperature in the range from 2700 K to 7800 K. Standard fluorescents are usually used for growing vegetables and herbs indoors or for starting seedlings to get a jump start on spring plantings. Standard fluorescents produce twice as many lumens per watt of energy consumed as incandescents and have an average usable life span of up to 20,000 hours. Cool white fluorescent lights are sometimes used as grow lights. These offer slightly lower performance, a white light, and lower purchase cost.
High-output Fluorescent lights produce twice as much light as standard fluorescent lights. A HO fluorescent fixture has a very thin profile, making it extremely useful in vertically limited areas. High-output fluorescents produce about 5,000 lumens per 54 watt bulb and are available in warm (2700 K) and cool (6500 K) versions. Usable life span for high-output fluorescent lights is about 10,000 hours.
Compact Fluorescent lights are smaller versions of fluorescent lights used for propagation, as well as for growing larger plants. Compact fluorescents work in specially designed reflectors that direct light to plants, much like HID lights. Compact fluorescent bulbs are also available in warm/red (2700 K), full spectrum or daylight (5000 K) and cool/blue (6500 K) versions. Usable life span for compact fluorescent grow lights is about 10,000 hours.
High-output fluorescent/high-intensity discharge hybrids combine cool operation with the penetration of high intensity discharge technology. The primary advantages to these fixtures is their blend of light colors and broad even coverage and reduced electric requirements.
High pressure sodium lights yield yellow lighting (2200 K) and have a very poor color rendering index of 22. They are used for the second (or reproductive) phase of the growth. If high pressure sodium lights are used for the vegetative phase, plants will usually grow slightly more quickly. The major drawback to growing under high pressure sodium alone is that the plants tend to be taller and leggier with a longer internodal length than plants grown under metal halide bulbs. High pressure sodium lights enhance the fruiting and flowering process in plants. Plants use the orange/red spectrum HPS in their reproductive processes, which produces larger harvests of higher quality herbs, vegetables, fruits or flowers. Sometimes the plants grown under these lights do not appear healthy due to the poor color rendering of high pressure sodium, which makes the plants look pale, washed out or nitrogen starved. High pressure sodium lighting have a long usable bulb life and six times more light output per watt of energy consumed than a standard incandescent grow light. Due to their high efficiency and the fact that plants grown in greenhouses get all the blue light they need naturally, these lights are the preferred supplemental greenhouse lights. But, in the higher latitudes, there are periods of the year where sunlight is scarce, and additional sources of light are indicated for proper growth. HPS lights may cause distinctive infrared and optical signatures, which can attract insects or other species of pests; these may in turn threaten the plants being grown. High pressure sodium lights emit a lot of heat which can cause leggier growth, although this can be controlled by using special air cooled bulb reflector/enclosures.
Combination HPS/MH lights combine a metal halide bulb and a high pressure sodium bulb in the same reflector, either with a single integrated ballast assembly or two separate ballast assemblies. The combination of blue metal halide light and red high pressure sodium light is said by manufacturers to create an ideal spectral blend and extremely high outputs, but in reality it is a compromise on both situations. These types of lights cost more than a standard light and have a shorter life span. Also because they use two smaller lights rather than one larger light the distance that the light penetrates is significantly shorter, in comparison to a regular hid bulb, due to the inverse-square law of light.
Switchable, two-way and convertible lights burn either a metal halide bulb or an equivalent wattage high pressure sodium bulb in the same fixture, but not at the same time. Growers use these fixtures for propagating and vegetatively growing plants under the metal halide, then switching to a high pressure sodium bulb for the fruiting or flowering stage of plant growth. To change between the lights, only the bulb needs changing and a switch needs to be set to the appropriate setting. These are commonly known as conversion bulbs and usually a metal halide conversion bulb will be used in an HPS ballast since the MH conversion bulbs are more common.
Recent advancements in LEDs allow production of relatively inexpensive, bright, and long-lasting grow lights that emit only the wavelengths of light corresponding to the absorption peaks of a plant's typical photochemical processes. Compared to other types of grow lights, LEDs are attractive to indoor growers since they consume much less electrical power, do not require ballasts, and produce considerably less heat. This allows LEDs to be placed closer to the plant canopy than other lights. Also, plants transpire less, as a result of the reduction in heat, and thus the time between watering cycles is longer.
There are multiple absorption peaks for chlorophyll and carotenoids, and LED grow-lights may use one or more LED colors overlapping these peaks.
Recommendations for optimal LED designs vary widely. According to one source, to maximize plant growth and health using available and affordable LEDs, U.S. patent #6921182 from July 2005 claims that "the proportion of twelve red 660 nm LEDs, plus six orange 612 nm LEDs and one blue 470 nm LED was optimal", such that the ratio of blue light to red & orange light is 6-8%.
It is also often published that for vegetative growth, blue LEDs are preferred, where the light has a wavelength somewhere in the mid-400 nm (nanometers). For growing fruits or flowers, a greater proportion of deep-red LEDs is considered preferable, with light very near 660 nm, the exact number this wavelength being much more critical than for the blue LED.
Early LED grow lights used hundreds of fractional-watt LEDs and were often not bright enough and/or efficient enough to be effective replacements for HID lights. Newer advanced LED grow lights may use high-brightness multiple-watt LEDs, with growing results similar to HID lights.
LED Grow Light LED's are increasing in power consumption resulting in increased effectiveness of the technology. LED's used in previous designs were 1 Watt in Power, however 3 Watt and even 5 Watt LED's are now commonly used in LED Grow Lights.
The plants' specific needs determine which lighting is most appropriate for optimum growth; artificial light must mimic the natural light to which the plant is best adapted. The bigger the plant gets the more light it requires; if there is not enough light, a plant will not grow, regardless of other conditions.
For example, vegetables grow best in full sunlight and to flourish indoors they need equally high light levels; thus fluorescent lights or MH-lights are best. Foliage plants (e.g., Philodendron) grow in full shade and can grow normally with much lower light levels, thus regular incandescents may already suffice).
In addition, plants also require both dark and light ("photo"-) periods. Therefore, lights may to be timed to turn them on and off at set times. The optimum photo/dark period depends on the species and variety of plant, as some prefer long days and short nights and others prefer the opposite, or intermediate "day lengths".
Illuminance, or luminous flux density, measured in lux is an important factor in indoor growing. Illuminance is the amount of light incident on a surface. One lux equals one lumen of light falling on an area of one square meter (lm/m2), which is approx. 0.093 foot-candle (lm/ft2). A brightly lit office would be illuminated at about 400 lux.
Lux are photometric units, in that different wavelengths of light are weighted by the eye's response to them; in professional farming, radiometric (watt/metre2 or microeinstein /second·meter2) or photosynthetically active radiation weighted (PAR watt) units are used instead.
A flashtube, also called a flashlamp, is an electric arc lamp designed to produce extremely intense, incoherent, full-spectrum white light for very short durations. Flashtubes are made of a length of glass tubing with electrodes at either end and are filled with a gas that, when triggered, ionizes and conducts a high voltage pulse to produce the light. Flashtubes are used mostly for photographic purposes but are also employed in scientific, medical and industrial applications.
The lamp comprises a hermetically sealed glass tube, which is filled with a noble gas, usually xenon, and electrodes to carry electrical current to the gas. Additionally, a high voltage power source is necessary to energize the gas. A charged capacitor is usually used for this purpose so as to allow very speedy delivery of very high electrical current when the lamp is triggered.
The glass envelope is most commonly a thin tube, often made of fused quartz, borosilicate or Pyrex, which may be straight, or bent into a number of different shapes, including helical, "U" shape, and circular (to surround a camera lens for shadowless photography—'ring flashes'). In some applications the emission of ultraviolet light is undesired, whether due to production of ozone, damage to laser rods, degradation of plastics, or other detrimental effects. In these cases a doped fused silica is used. Doping with titanium dioxide can provide different cutoff wavelengths on the ultraviolet side, but the material suffers from solarization; it is often used in medical and sun-ray lamps and some non-laser lamps. A better alternative is a cerium-doped quartz; it does not suffer from solarization and has higher efficiency, as part of the absorbed ultraviolet is reradiated as visible via fluorescence. Its cutoff is at about 380 nm. Conversely, when ultraviolet is called for, a synthetic quartz is used as the envelope; it is the most expensive of the materials, but it is not susceptible to solarization and its cutoff is at 160 nm.
The electrodes protrude into each end of the tube, and are sealed to the glass using a few different methods. "Ribbon seals" use thin strips of molybdenum foil bonded directly to the glass, which are very durable, but are limited in the amount of current that can pass through. "Solder seals" bond the glass to the electrode with a solder for a very strong mechanical seal, but are limited to low temperature operation. Most common in laser pumping applications is the "rod seal", where the rod of the electrode is wetted with another type of glass and then bonded directly to a quartz tube. This seal is very durable and capable of withstanding very high temperature and currents.
For low electrode wear the electrodes are usually made of tungsten, which has the highest melting point of any metal, to handle the thermionic emission of electrons. Cathodes are often made from porous tungsten filled with a barium compound, which gives low work function; the structure of cathode has to be tailored for the application. Anodes are usually made from pure tungsten, or, when good machinability is required, lanthanum-alloyed tungsten, and are often machined to provide extra surface area to cope with power loading. DC arc lamps often have a cathode with a sharp tip, to help keep the arc away from the glass and to control temperature. Flashtubes usually have a cathode with a flattened radius, to reduce the incidence of hot spots and decrease sputter caused by peak currents, which may be in excess of 1000 amperes. Electrode design is also influenced by the average power. At high levels of average power, care has to be taken to achieve sufficient cooling of the electrodes. While anode temperature is of lower importance, overheating the cathode can greatly reduce the lamp's lifetime.
The power level of the lamps is rated in watts/area, total output power divided by the lamp's surface. Cooling of the electrodes and the lamp envelope is of high importance at high power levels. Air cooling is sufficient for lower average power levels. High power lamps are cooled with a liquid, typically by flowing demineralized water through a tube in which the lamp is encased. The cooling medium should flow also over the ends of the lamps, seals and electrodes. Above 15 W/cm2 forced air cooling is required, liquid cooling if in a confined space. Liquid cooling is generally necessary above 30 W/cm2. Thinner walls can survive higher power loads due to lower mechanical strain across the thickness of the material; e.g. 1mm thick doped quartz has limit of 160 W/cm2, 0.5mm thick one has limit of 320 W/cm2. The material of the envelope provides another limit for the output power; 1mm thick fused quartz has a limit of 200 W/cm2, synthetic quartz of same thickness can run up to 240 W/cm2. Aging lamps require some derating, due to increased energy absorption in the glass due to solarization and sputtered deposits.
Depending on the size, type, and application of the flashtube, gas fill pressures may range from a few kilopascals to hundreds of kilopascals (0.01–4.0 atmospheres or tens to thousands of torr). Generally, the higher the pressure, the greater the output efficiency. Xenon is used mostly because of its good efficiency, converting nearly 50% of electrical energy into light. Krypton, on the other hand, is only about 40% efficient, but at low currents is a better match to the absorption spectrum of Nd:YAG lasers. A major factor affecting efficiency is the amount of gas behind the electrodes, or the "dead volume". A higher dead volume leads to a lower pressure increase during operation.
The electrodes of the lamp are usually connected to a capacitor, which is charged to a relatively high voltage (generally between 250 and 5000 volts), using a step up transformer and a rectifier. The gas, however, exhibits extremely high resistance, and the lamp will not conduct electricity until the gas is ionized. Once ionized, or "triggered", a spark will form between the electrodes, allowing the capacitor to discharge. The sudden surge of electric current quickly heats the gas to a plasma state, where electrical resistance becomes very low. There are several methods of triggering.
External triggering is the most common method of operation, especially for photographic use. The electrodes are charged to a voltage high enough to respond to triggering, but below the lamp's self-flash threshold. An extremely high voltage pulse, (usually between 2000 and 150,000 volts), the "trigger pulse", is applied directly to, or very near, the glass envelope. (Water cooled flashtubes sometimes apply this pulse directly to the cooling water, and often to the housing of the unit as well, so care must be taken with this type of system.) The short, high voltage pulse creates a rising electrostatic field, which ionizes the gas inside the tube. The capacitance of the glass couples the trigger pulse into the envelope, where it exceeds the breakdown voltage of the gas surrounding one or both of the electrodes, forming spark streamers. The streamers propagate via capacitance along the glass at a speed of 1 centimeter in 60 nanoseconds (=170 km/s) . (A trigger pulse must have a long enough duration to allow one streamer to reach the opposite electrode, or erratic triggering will result.) The triggering can be enhanced by applying the trigger pulse to a "reference plane", which may be in the form of a metal band or reflector affixed to the glass, a conductive paint, or a thin wire wrapped around the length of the lamp. When the internal spark streamers bridge the electrodes, the capacitor discharges through the ionized gas, heating the xenon to a high enough temperature for the emission light.
Series triggering is more common in high powered, water cooled flashtubes, such as those found in lasers. The high voltage leads of the trigger-transformer are connected to the flashtube in series, (one lead to an electrode and the other to the capacitor). The trigger pulse forms a spark inside the lamp, without exposing the trigger voltage to the outside of the lamp. The advantages are better insulation, more reliable triggering, and an arc that tends to develop well away from the glass, but at a much higher cost.
Simmer voltage triggering is the least common method. In this technique, the capacitor voltage is not initially applied to the electrodes, but instead, a high voltage spark streamer is maintained between the electrodes. The high current from the capacitor is delivered to the electrodes using a thyristor or a spark gap. This type of triggering is used mainly in very fast rise time systems, typically those that discharge in the microsecond regime, such as used in high speed stop-motion photography, or dye lasers. If external triggering is used, the spark streamers may still be in contact with the glass when the full current load passes through the tube, causing wall ablation, or in extreme cases, cracking or even explosion of the lamp. Some microsecond flashtubes are triggered by simply "over-volting", that is, by applying a voltage to the electrodes which is much higher than the lamp's self-flash threshold, using a spark gap.
In addition, an insulated-gate bipolar transistor (IGBT) can be connected in series with both the trigger transformer and the lamp, making adjustable flash durations possible. An IGBT used for this purpose must be rated for a high pulsed current, so as to avoid over-current damage to the semiconductor junction. This type of system is used frequently in high average power laser systems, and can produce pulses ranging from 500 microseconds to over 20 milliseconds. It can be used with any of the triggering techniques, like external and series, and can produce square wave pulses. It can even be used with simmer voltage to produce a "modulated" continuous wave output, with repetition rates over 300 hertz. With the proper large bore, water cooled flashtube, several kilowatts of average power output can be obtained.
The electrical requirements for a flashtube can vary, depending on the desired results. The usual method, once maximum power and the safe amount of operating energy is determined, is to pick a current density that will emit the desired spectrum, and let the lamp's resistance determine the necessary combination of voltage and capacitance to produce it. The resistance in flashtubes varies greatly, depending on pressure, shape, dead volume, current density, time, and flash duration, and therefore, is usually referred to as impedance. The most common symbol used for lamp impedance is Ko, which is expressed as ohms(amps0.5).
As with all ionized gases, xenon flashtubes emit light in various spectral lines. This is the same phenomenon that gives neon signs their characteristic color. However, neon signs emit red light because of extremely low current densities when compared to those seen in flashtubes, which favors spectral lines of longer wavelengths . Higher current densities tend to favor shorter wavelengths. The light from xenon, in a neon sign, likewise is rather violet.
The spectrum emitted by flashtubes is far more dependent on current density than on the fill pressure or gas type. Low current densities produce spectral line emission, against a faint background of continuous radiation. Xenon has many spectral lines in the UV, blue, green, red, and IR portions of the spectrum. Low current densities produce a greenish-blue flash, indicating the absence of significant yellow or orange lines. At low current densities, most of xenon's output will be directed into the invisible IR spectral lines around 820, 900, and 1000 nm. Low current densities for flashtubes are generally less than 1000 A/cm2.
Higher current densities begin to produce continuum emission. Spectral lines are less dominant as light is produced across the spectrum, usually peaking, or "centered", on a certain wavelength. Optimum output efficiency in the visual range is obtained at a density that favors "greybody radiation" (an arc that produces mostly continuum emission, but is still mostly transparent to its own light). For xenon, greybody radiation is centered near green, and produces the right combination for white light. Greybody radiation is produced at densities above 2400 A/cm2.
Current densities that are very high, approaching 4000 A/cm2, tend to favor blackbody radiation. As current densities become even higher, xenon's output spectrum will begin to settle on that of a blackbody radiator with a color temperature of 9800 kelvins (a rather sky-blue shade of white). Blackbody radiation is usually not desired, because much of the radiation from within the arc can be absorbed before reaching the surface, impairing output efficiency.
Due to its high efficient white output, xenon is used extensively for photographic applications, despite its great expense. In lasers, spectral line emission is usually favored, as these lines tend to better match absorption lines of the lasing media. Krypton is also occasionally used, although it is even more expensive. At low current densities, krypton's spectral line output in the near-IR range is better matched to the absorption profile of neodymium based laser media than xenon emission, and very closely matches the narrow absorption profile of Nd:YAG.
An extensive study was done in the 1960s on the characteristics of other gases when operated in flashtubes. All gases produce spectral lines which are specific to the gas, superimposed on a background of continuum radiation. Like xenon, low current densities produce mostly spectral lines, with the highest output being concentrated in the near-IR between 650 and 1000 nm. Krypton's strongest peaks are around 760 and 810 nm. Argon has many strong peaks at 670, 710, 760, 820, 860, and 920 nm. Neon has peaks around 650, 700, 850, and 880 nm. As current densities become higher, the output of continuum radiation will increase more than the spectral line radiation at a rate 20% greater, and output center will shift toward the visual spectrum. At greybody current densities there is only a slight difference in the spectrum emitted by various gases. At very high current densities, all gases will begin to operate as blackbody radiators, with spectral outputs centered in the near-UV.
Heavier gases exhibit higher resistance, and therefore, have a higher value for Ko. Impedance, being defined as the resistance required to change energy into work, is higher for heavier gases, and as such, the heavier gases are much more efficient than the lighter ones. Helium and neon are far too light to produce an efficient flash. Krypton can be as good as 40% efficient, but requires up to a 70% increase in pressure to achieve this. Argon can be up to 30% efficient, but requires an even greater pressure increase. At such high pressures, the voltage drop between the electrodes, formed by the spark streamer, may be greater than the capacitor voltage. These lamps often need a "boost voltage" during the trigger phase, to overcome the extremely high trigger impedance.
Nitrogen, in the form of air, has been used in flashtubes in home made dye lasers, but the nitrogen and oxygen present form chemical reactions with the electrodes, and themselves, causing premature wear and the need to adjust the pressure for each flash.
Some research has been done on mixing gases to alter the spectral output. The effect on the output spectrum is negligible, but the effect on efficiency is great. Adding a lighter gas will only reduce the efficiency of the heavier one.
As the current pulse travels through the tube, it ionizes the atoms, causing them to jump to higher energy levels. Three types of particles are found within the arc plasma, consisting of electrons, positively ionized atoms, and neutral atoms. At any given time, the ionized atoms make up less than 1% of the plasma and produce all of the emitted light. As they recombine with their lost electrons they immediately drop back to a lower energy state, releasing photons in the process. The methods of transferring energy occur in three separate ways, called "bound-bound," "free-bound," and "free-free" transitions.
Within the plasma, positive ions move toward the cathode while electrons and neutral atoms move toward the anode. Bound-bound transitions occur when the ions and neutral atoms collide, transferring an electron from the atom to the ion. This method predominates at low current densities, and is responsible for producing the spectral line emission. Free-bound transitions happen when an ion captures a free electron. This method produces the continuum emission, and is more prominent at higher current densities. Some of the continuum is also produced when an electron accelerates toward an ion, called free-free transitions, producing bremsstrahlung radiation.
For short pulses the only real electrical limit is the total system inductance, including that of the capacitor. Short pulse flashes require that all inductance be minimized. The amount of power loading the glass can handle is the major mechanical limit. Although the amount of energy, or joules, that is used remains constant, electrical power, or wattage, increases in inverse proportion to a decrease in discharge time. Quartz glass, 1 millimeter thick, can usually withstand a maximum of 160 watts per square centimeter of internal surface area. Other glasses have a much lower threshold. Extremely fast systems, with inductance below 0.8 microhenries, usually require a shunt diode across the capacitor, to prevent current reversal from destroying the lamp.
The limits to long pulse durations are the number of transferred electrons to the anode, sputter caused by ion bombardment at the cathode, and the temperature gradients of the glass. For continuous operation the cooling is the limit. Discharge durations for common flashtubes range from 1 microsecond to tens of milliseconds, and can have repetition rates of hundreds of hertz. Flash duration can be carefully controlled with the use of an inductor.
The flash that emanates from a xenon flashtube may be so intense that it can ignite flammable materials within a short distance of the tube. Carbon nanotubes are particularly susceptible to this spontaneous ignition when exposed to the light from a flashtube. Similar effects may be exploited for use in aesthetic or medical procedures known as intense pulsed light (IPL) treatments. IPL can be used for treatments such as hair removal and destroying lesions or moles.
The lifetime of a flashtube depends on both the energy level used for the lamp in proportion to its explosion energy, and on the pulse duration of the lamp. Failures can be catastrophic, causing the lamp to shatter, or they can be gradual, reducing the performance of the lamp below a usable rating.
Catastrophic failure can occur from two separate mechanisms; energy and heat. When too much energy is used for the pulse duration, structural failure of the glass envelope can occur. Flashtubes produce an electrical arc contained in a glass tube. As the arc develops a supersonic shock wave forms, traveling radially from the center of the lamp and impacting the inner wall of the tube. If the energy level used equals the "explosion energy" rating of the lamp, the impacting shock wave will fracture the glass, rupturing the tube. The resulting explosion creates a loud sonic shock wave, and may throw shattered glass several feet. The explosion energy is calculated by multiplying the internal surface area of the lamp with the power loading capacity of the glass. Power loading is determined by the type and thickness of the glass, and the cooling method that is used. Power loading is measured in watts per centimeter squared. However, since the pulsed power level increases as the flash duration decreases, the explosion energy must then be decreased in direct proportion to the square root of discharge time.
Failure from heat is usually caused by excessively long pulse durations or high average power levels. When the inner wall of the tube gets too hot while the outer wall is still cold, this temperature gradient can cause the lamp to crack. Similarly, if the electrodes heat much faster than the glass, the lamp may crack or even shatter at the ends.
The closer a flashtube operates to its explosion energy, the greater the risk becomes for catastrophic failure. At 50% of the explosion energy, the lamp may produce several thousand flashes before exploding. At 60% of the explosion energy, the lamp will usually fail in less than a hundred. If the lamp is operated below 30% of the explosion energy the risk of catastrophic failure becomes very low. The methods of failure then become those that reduce the output efficiency and affect the ability to trigger the lamp. The processes affecting these are sputter and ablation of the inner wall.
Sputter occurs when the energy level is very low, below 15% of the explosion energy, or when the pulse duration is very long. Sputter is the vaporization of metal from the cathode, which is redeposited on the walls of the lamp, blocking the light output. Since the cathode is more emissive than the anode, the flashtube is polarized, and connecting the lamp to the power source incorrectly will quickly ruin it. It is impossible to predict the lifetime accurately at low energy levels.
At higher energy levels, wall ablation becomes the main process of wear. The electrical arc slowly erodes the inner wall of the tube, forming microscopic cracks that give the glass a frosted appearance. The ablation releases oxygen from the glass, increasing the pressure beyond an operable level. This causes triggering problems, known as "jitter". However, at higher energy levels the lifetime can be calculated with a fair degree of accuracy.
Because the duration of the flash that is emitted by a xenon flashtube can be accurately controlled, and due to the high intensity of the light, xenon flashtubes are commonly used as photographic strobe lights. Xenon flashtubes are also used in the technique of very high speed or "stop-motion" photography, which was pioneered by Harold Edgerton in the 1930s. Because they can generate bright, attention-getting flashes with a relatively small continuous input of electrical power, they are also used in warning lights, emergency vehicle lighting, fire alarm annunciator devices (horn lights), aircraft anticollision beacons, and other similar applications.
Due to their high-intensity and relative brightness at short wavelengths (extending into the ultraviolet) and short pulse widths, flashtubes are also ideally suited as light sources for pumping atoms in a laser to excited states where they can subsequently be stimulated to emit coherent monochromatic light. Proper selection of the filler gas is crucial here, so the maximum of radiated output energy is concentrated in the bands that are the best absorbed by the lasing medium; e.g. krypton flashtubes are more suitable than xenon flashtubes for pumping Nd:YAG lasers, as krypton emission in near infrared is better matched to the absorption spectrum of Nd:YAG.
Xenon flashtubes have been used to produce an intense flash of white light, some of which is absorbed by Nd:glass that produces the laser power for inertial confinement fusion. In total about 1 to 1.5% of the electrical power fed into the flashtubes is turned into useful laser light for this application.
The flashtube was invented by Harold Edgerton in the 1930s as a means to take sharp photographs of moving objects. Flashtubes were mainly used for strobe lights in scientific studies, but eventually began to take the place of chemical and powder flash lamps in mainstream photography.
Early high-speed photographs were taken with an open-air electrical arc discharge, called spark photography. The earliest known use of spark photography began with Henry Fox Talbot around 1850. In 1886, Ernst Mach used an open air spark to photograph a speeding bullet, revealing the shockwaves it produced at supersonic speeds. Open air spark systems were fairly easy to build, but were bulky, very limited in light output, and produced loud noises comparable to that of the gunshot.
In 1927, Harold Edgerton built his first flash unit while at MIT. Wanting to photograph the motion of a motor in vivid detail, without blur, Edgerton decided to improve the process of spark photography by using a mercury-arc rectifier instead of an open air discharge to produce the light. He was able to achieve a flash duration of 10 microseconds, and was able to photograph the moving motor as if "frozen in time."
Interest in the new flash apparatus soon provoked Edgerton to improve upon the design. The mercury lamps were only as efficient as the warmest part of the lamp, causing them to perform better when very hot but poorly when cold. Edgerton decided that a noble gas would not be as temperature dependent and, in 1930, he employed the General Electric company to construct some lamps using argon instead. The argon lamps were much more efficient, compact, and could be mounted near a reflector, concentrating their output. Slowly, camera designers began to take notice of the new technology and began to accept it. Edgerton received his first major order for the strobes from the Kodak company in 1940. Afterward, he discovered that xenon was the most efficient of the noble gases, producing a spectrum very close to that of daylight, and xenon flashtubes became standard in most large photography sets. It was not until the 1970s that strobe units became portable enough to use in common cameras.
In 1960, after Theodore Maiman invented the ruby laser, a new demand for flashtubes began for use in lasers, and new interest was taken in the study of the lamps.
Flashtubes operate at high voltages, with currents high enough to be deadly. Shocks as low as 1 joule have been reported to be lethal. The energy stored in a capacitor can remain surprisingly long after power has been disconnected. A flashtube will usually shut down before the capacitor has fully drained, and it may regain part of its charge through a process called "dielectric absorption". In addition, the charging system itself can be equally deadly. The trigger voltage can deliver a painful shock, usually not enough to kill, but which can often startle a person into bumping or touching something more dangerous. At high voltages a spark can jump, delivering the high capacitor current without even touching anything.
Flashtubes operate at high pressures and are known to explode, producing violent shockwaves. The "explosion energy" of a flashtube (the amount of energy that will destroy it in just a few flashes) is well defined, and to avoid catastrophic failure, it is recommended that no more than 30% of the explosion energy be used. Flashtubes should be shielded behind glass or in a reflector cavity. If not, eye and ear protection should be worn.
Flashtubes produce very intense flashes, often faster than the eye can register, and may not appear as bright as they are. Quartz glass will transmit nearly all of the long and short wave UV, including the germicidal wavelengths, and can be a serious hazard to eyes and skin. This ultraviolet radiation can also produce large amounts of ozone, which can be harmful to people, animals, and equipment.
Many compact cameras charge the flash capacitor immediately after power-up, and some even just by inserting the batteries. Merely inserting the battery into the camera can prime the capacitor to become dangerous or at least unpleasant for up to several days. The energy involved is also fairly significant; a 330 microfarad capacitor charged to 300 volts (common ballpark values found in cameras) stores almost 15 joules of energy.
Frame 1: The trigger pulse ionizes the gas. Spark streamers form.
Frame 2: Spark streamers connect and move away from the glass, as amperes surge.
Frame 3: Capacitor current begins to flow, heating the surrounding xenon.
Frame 4: As resistance decreases current fills the tube, heating the xenon to a plasma state.
Frame 5: Fully heated, the full current load rushes through the tube and the xenon emits a burst of light.
In the 1969 book The Andromeda Strain and the 1971 motion picture, specialized exposure to a xenon flash apparatus was used to burn off the outer epithelial layers of human skin as an antiseptic measure to eliminate all possible bacterial access for persons working in an extreme ultraclean environment. (The book used the term 'ultraflash'; the movie identified the apparatus as a 'xenon flash'.)
A strobe light or stroboscopic lamp, commonly called a strobe, is a device used to produce regular flashes of light. It is one of a number of devices that can be used as a stroboscope. The word originated from the Greek strobos, meaning "act of whirling."
Strobe lights are used in scientific and industrial applications, in clubs where they are used to give an illusion of slow motion (cf. stroboscopic effect) and for aircraft anti-collision lighting. Other applications are in alarm systems, theatrical lighting (most notably to simulate lightning), and as high-visibility running lights. They are still widely used in law enforcement and other emergency vehicles, though they are slowly being replaced by LED technology in this application, as they themselves largely replaced halogen lighting. Strobes are used by scuba divers as an emergency signaling device. Strobe lighting has also been used to see the movements of the vocal cords in slow motion during speech, a procedure known as video-stroboscopy. Special calibrated strobe lights, capable of flashing up to hundreds of times per second, are used in industry to "stop" the motion of rotating and other repetitively-operating machinery and to measure, or adjust, the rotation speeds or cycle times. Since this stop is only apparent, a marked point on the rotating body will either appear to move backward or forward, or not move, depending on the frequency of the strobe-flash. If the flash occurs equal to the period of rotation (or evenly multiplied or divided, i.e. n*ω or ω/n, where n is an integer and ω the angular frequency) the marked point will appear to not move. Any non integer flash setting will make the mark appear to move forward or backward, e.g. a slight increase of the flash frequency will make the point appear to move backward. A common use of a strobe flash is to optimize a car engine's efficiency at a certain rotational period by directing the strobe-light towards a mark on the fly-wheel on the engine's main axle. The strobe-light tool for such ignition timing is called a timing light.
Strobelights are often used in nightclubs and raves, and are available for home use for special effects or entertainment.
A typical commercial strobe light has a flash energy in the region of 10 to 150 joules, and discharge times as short as a few milliseconds, often resulting in a flash power of several kilowatts. Larger strobe lights can be used in “continuous” mode, producing extremely intense illumination.
The light source is commonly a xenon flash lamp, which has a complex spectrum and a color temperature of approximately 5,600 kelvins. To obtain colored light, colored gels must be used.
A strobe light typically uses a capacitor, an energy storage device much like a battery, but capable of charging and releasing energy much faster. Recently, some strobe lights have been found to use rectified mains electricity and no capacitors at all. In a capacitor based strobe light, the capacitor is charged up to around 300V. Once the capacitor has been charged, a small amount of power is diverted into a trigger transformer, a small transformer with a high turns ratio, which generates a weak, but high voltage spike required to ionize the xenon gas in a flash tube. An arc is created inside the tube, which acts as a bridge for the much bigger pulse to flow down later. Arcs present almost a direct short circuit, allowing the capacitors to quickly release their energy into the arc. This rapidly heats the xenon gas, creating an extremely bright plasma discharge, which is seen as a flash.
A strobe without a capacitor storage device simply discharges mains voltages across the tube once it's fired. This method means no charging times are required, and flash rates can be much faster, but drastically reduce the lifetime of the flash tube if powered for excess amounts of time. These strobes require a form of current limiting, as mentioned before, an arc acts as a short circuit. If this current limiting was eliminated, the flash tube would attempt to draw high currents from the electricity source, potentially tripping electrical breakers or causing voltage drops in the power supply line.
A strobe flash typically lasts around 200 microseconds, however can be faster or slower depending on the use of the strobe. Some strobes even offer continuous mode, where the arc is sustained, providing and extremely high intensity light, but usually only for small amounts of time to prevent overheating of the flash tube and thus breakage.
The origin of strobe lighting dates to 1931, when Harold Eugene "Doc" Edgerton employed a flashing lamp to make an improved stroboscope for the study of moving objects, eventually resulting in dramatic photographs of objects such as bullets in flight.
EG&G [now a division of URS] was founded by Harold E. Edgerton, Kenneth J. Germeshausen and Herbert E. Grier in 1947 as Edgerton, Germeshausen and Grier, Inc. and today bears their initials. In 1931, Edgerton and Germeshausen had formed a partnership to study high-speed photographic and stroboscopic techniques and their applications. Grier joined them in 1934, and in 1947, EG&G was incorporated. During World War II, the government's Manhattan Project made use of Edgerton's discoveries to photograph atomic explosions; it was a natural evolution that the company would support the Atomic Energy Commission in its weapons research and development after the war. This work for the Commission provided the historic foundation to the Company's present-day technology base.
The strobe light was popularized on the club scene during the 1960s when it was used to reproduce and enhance the effects of LSD trips. Ken Kesey used strobe lighting in coordination with the music of the Grateful Dead during his legendary Acid Tests.
Strobe lighting can trigger seizures in photosensitive epilepsy. An infamous event took place in 1997 in Japan when an episode of the Pokémon anime, Dennō Senshi Porygon, featured a scene that depicted a huge explosion using flashing red and blue lights, causing about 685 of the viewing children to be sent to hospitals. These flashes were extremely bright strobe lights.
Most strobe lights on sale to the public are factory-limited to about 10-12 flashes per second in their internal oscillators, although externally triggered strobe lights will often flash as frequently as possible. At a frequency of 10 Hz, 65% of affected people are still at risk. The British Health and Safety Executive recommend that a net flash rate for a bank of strobe lights does not exceed 5 flashes per second, at which only 5% of photosensitive epileptics are at risk. It also recommends that no strobing effect continue for more than 30 seconds, due to the potential for discomfort and disorientation.
Neon lighting is created by brightly glowing, electrified glass tubes or bulbs that contain rarefied neon or other gases. Georges Claude, a French engineer and inventor, presented neon tube lighting in essentially its modern form at the Paris Motor Show from December 3–18, 1910. Claude, sometimes called "the Edison of France", had a near monopoly on the new technology, which became very popular for signage and displays in the period 1920-1940. Neon lighting was an important cultural phenomenon in the United States in that era; by 1940, the downtowns of nearly every city in the US were bright with neon signage, and Times Square in New York City was known worldwide for its neon extravagances. There were 2000 shops nationwide designing and fabricating neon signs. The popularity, intricacy, and scale of neon signage for advertising declined in the U.S. following the Second World War (1939–1945), but development continued vigorously in Japan, Iran, and some other countries. In recent decades architects and artists, in addition to sign designers, have again adopted neon tube lighting as a component in their works.
A second technology for neon lighting, the miniature neon glow lamp, was developed in 1917, about seven years after neon tube lighting. While neon tube lights are typically meters long, the lamps can be less than one centimeter in length and glow much more dimly than the tube lights. Through the 1970s, neon glow lamps were widely used for displays in electronics, for small decorative lamps, and as electronic devices in of themselves. While these lamps are now antiques, the technology of the neon glow lamp developed into contemporary plasma displays and televisions.
Neon lighting is closely related to fluorescent lighting, which developed about 25 years after neon tube lighting. In fluorescent lights, the light emitted by rarefied gases within a tube is used exclusively to excite fluorescent materials that coat the tube, which then shine with their own colors that become the tube's visible, usually white, glow. Fluorescent coatings and glasses are also an option for neon tube lighting, but are usually selected to obtain bright colors.
Neon is a chemical element and an inert gas that is a minor component of the Earth's atmosphere. It was discovered in 1898 by William Ramsey and Morris W. Travers. When Ramsey and Travers had succeeded in obtaining some pure neon from the atmosphere, they explored its properties using an "electrical gas-discharge" tube that was similar to the tubes used today for neon signs. Travers later wrote, "the blaze of crimson light from the tube told its own story and was a sight to dwell upon and never forget." The procedure of examining the colors of the light emitted from gas-discharge (or "Geissler" tubes) was well-known at the time, since the colors of light (the "spectral lines") emitted by a gas discharge tube are, essentially, fingerprints that identify the gases inside.
Immediately following neon's discovery, neon tubes were used as scientific instruments and novelties. However, the scarcity of purified neon gas precluded its prompt application for electrical gas-discharge lighting along the lines of Moore tubes, which used more common nitrogen or carbon dioxide as the working gas, and enjoyed some commercial success in the US in the early 1900s. After 1902, Georges Claude's company in France, Air Liquide, began producing industrial quantities of neon essentially as a byproduct of the air liquefaction business. From December 3–18, 1910, Claude demonstrated two large (12 metres (39 ft) long), bright red neon tubes at the Paris Motor Show.
These neon tubes were essentially in their contemporary form. The range of outer diameters for the glass tubing used in neon lighting is 9 to 25 mm; with standard electrical equipment, the tubes can be as long as 30 metres (98 ft). The pressure of the gas inside is in the range 3-20 Torr (0.4-3 kPa), which corresponds to a partial vacuum in the tubing. Claude had also solved two technical problems that substantially shortened the working life of neon and some other gas discharge tubes, and effectively gave birth to a neon lighting industry. In 1915 a US patent was issued to Claude covering the design of the electrodes for gas-discharge lighting; this patent became the basis for the monopoly held in the US by his company, Claude Neon Lights, for neon signs through the early 1930s.
Claude's patents envisioned the use of gases such as argon and mercury vapor to create different colors beyond those produced by neon. In the 1920s, fluorescent glasses and coatings were developed to further expand the range of colors and effects for tubes with argon gas or argon-neon mixtures; generally, the fluorescent coatings are used with an argon/mercury-vapor mixture, which emits ultraviolet light that activates the fluorescent coatings. By the 1930s, the colors from combinations of neon tube lights had become satisfactory for some general interior lighting applications, and achieved some success in Europe, but not in the US. Since the 1950s, the development of phosphors for color televisions has created nearly 100 new colors for neon tube lighting.
Around 1917, Daniel McFarlan Moore, then working at the General Electric Company, developed the miniature neon lamp. The glow lamp has a very different design than the much larger neon tubes used for signage; the difference was sufficient that a separate US patent was issued for the lamp in 1919. A Smithsonian Institution website notes, "These small, low power devices use a physical principle called "coronal discharge." Moore mounted two electrodes close together in a bulb and added neon or argon gas. The electrodes would glow brightly in red or blue, depending on the gas, and the lamps lasted for years. Since the electrodes could take almost any shape imaginable, a popular application has been fanciful decorative lamps. Glow lamps found practical use as electronic components, and as indicators in instrument panels and in many home appliances until the acceptance of Light-Emitting Diodes (LEDs) starting in the 1970s."
Although some neon lamps themselves are now antiques, and their use in electronics has declined markedly, the technology has continued to develop in artistic and entertainment contexts. Neon lighting technology has been reshaped from long tubes into thin flat panels used for plasma displays and plasma television sets.
When Georges Claude demonstrated an impressive, practical form of neon tube lighting in 1910, he apparently envisioned that it would be used as a form of lighting, which had been the application of the earlier Moore tubes that were based on nitrogen and carbon dioxide discharges. Claude's 1910 demonstration of neon lighting at the Grand Palais (Grand Palace) in Paris lit a peristyle of this large exhibition space. Claude's associate, Jacques Fonseque, realized the possibilities for a business based on signage and advertising. By 1913 a large sign for the vermouth Cinzano illuminated the night sky in Paris, and by 1919 the entrance to the Paris Opera was adorned with neon tube lighting.
Neon signage was received with particular enthusiasm in the United States. In 1923, Earle C. Anthony purchased two neon signs from Claude for his Packard car dealership in Los Angeles, California; these literally stopped traffic. Claude's US patents had secured him a monopoly on neon signage, and following Anthony's success with neon signs, many companies arranged franchises with Claude to manufacture neon signs. In many cases companies were given exclusive licenses for the production of neon signs in a given geographical area; by 1931, the value of the neon sign business was $16.9 million, of which a significant percentage was paid to Claude Neon Lights, Inc. by the franchising arrangements. Claude's principal patent expired in 1932, which led to a great expansion in the production of neon signage. The industry's sales in 1939 were about $22.0 million; the expansion in volume from 1931 to 1939 was much larger than the ratio of sales in the two years suggests.
Rudi Stern has written, "The 1930s were years of great creativity for neon, a period when many design and animation techniques were developed. ... Men like O. J. Gude and, in particular, Douglas Leigh took neon advertising further than Georges Claude and his associates had ever envisioned. Leigh, who conceived and created the archetypal Times Square spectacular, experimented with displays that incorporated smells, fog, and sounds as part of their total effect. ... Much of the visual excitement of Times Square in the thirties was a result of Leigh's genius as a kinetic and luminal artist." Major cities throughout the United States and in several other countries also had elaborate displays of neon signs. Events such as the Chicago Century of Progress Exposition (1933–34), the Paris World's Fair (1937) and New York World's Fair (1939) were remarkable for their extensive use of neon tubes as architectural features. Stern has argued that the creation of "glorious" neon displays for movie theaters led to an association of the two, "One's joy in going to the movies became inseparably associated with neon."
The Second World War (1939–1945) arrested new sign installations around most of the world. Following the war, the industry resumed. Marcus Thielen writes of this era, "...after World War II, government programs were established to help re-educate soldiers. The Egani Institute (New York City) was one of few schools in the country that taught neon-trade secrets. The American streamlined design from the 1950s would be unimaginable without the use of neon." The development of Las Vegas, Nevada as a resort city is inextricably linked with neon signage; Tom Wolfe wrote in 1965, "Las Vegas is the only city in the world whose skyline is made neither of buildings, like New York, nor of trees, like Wilbraham, Massachusetts, but signs. One can look at Las Vegas from a mile away on route 91 and see no buildings, no trees, only signs. But such signs! They tower. They revolve, they oscillate, they soar in shapes before which the existing vocabulary of art history is helpless."
Overall, however, neon displays became less fashionable, and some cities discouraged their construction with ordinances. Nelson Algren titled a 1947 collection of his short stories The Neon Wilderness. Margalit Fox has written, "... after World War II, as neon signs were replaced increasingly by fluorescent-lighted plastic, the art of bending colored tubes into sinuous, gas-filled forms began to wane." A dark age persisted at least through the 1970s, when artists adopted neon with enthusiasm; in 1979 Rudi Stern published his manifesto, Let There Be Neon. Marcus Thielen wrote in 2005, on the 90th anniversary of the US patent issued to Georges Claude, "The demand for the use of neon and cold cathode in architectural applications is growing, and the introduction of new techniques like fiberoptics and LED — into the sign market have strengthened, rather than replaced, neon technology. The evolution of the 'waste' product neon tube remains incomplete 90 years after the patent was filed."
In neon glow lamps, the luminous region of the gas is a thin, "negative glow" region immediately adjacent to a negatively charged electrode (or "cathode"); the positively charged electrode ("anode") is quite close to the cathode. These features distinguish the lamps from the much longer and brighter luminous regions in neon tube lighting; technically, the latter correspond to a "positive column" in the discharge that is absent in the lamps. The energy dissipation in the lamps when they are glowing is very low (about 0.1 W), hence the distinguishing term cold-cathode lighting.
Some of the applications of neon lamps include:
The small size of the negative glow region of a neon lamp, and the flexible electronic properties that were exploited in electronic circuits, led to the adoption of this technology for the earliest plasma panel displays. The first monochrome dot matrix plasma panel displays were developed in 1964 at the University of Illinois for the PLATO educational computing system. They had the characteristic color of the neon lamp; their inventors, Donald L. Bitzer, H. Gene Slottow, and Robert H. Wilson, had achieved a working computer display that remembered its own state, and did not require constant refreshing from the central computer system. The relationship between these early monochrome displays and contemporary, color plasma displays and televisions was described by Larry F. Weber in 2006, "All plasma TVs on the market today have the same features that were demonstrated in the first plasma display which was a device with only a single cell. These features include alternating sustain voltage, dielectric layer, wall charge, and a neon-based gas mixture." As in colored neon lamps, plasma displays use a gas mixture that emits ultraviolet light. Each pixel has a phosphor that emits one of the display's base colors.
The mid to late 1980's was a period of resurgence in neon production. Sign companies developed a new type of signage called channel lettering, in which individual letters were fashioned from sheet metal.
While the market for neon lighting in outdoor advertising signage has declined since the mid 20th Century, in recent decades neon lighting has been used consciously in art, both in individual objects and integrated into architecture. Frank Popper traces the use of neon lighting as the principal element in artworks to Gyula Košice's late 1940s work in Argentina. Among the later artists whom Popper notes in a brief history of neon lighting in art are Stephen Antonakos, the conceptual artists Joseph Kosuth and Bruce Nauman, Martial Raysse, Chryssa, Piotr Kowalski, and François Morellet.
Several museums in the United States are now devoted to neon lighting and art, including the Museum of Neon Art (founded by neon artist Lili Lakich, Los Angeles, 1981), the Neon Museum (Las Vegas, founded 1996), the American Sign Museum (Cincinnati, founded 1999), and the Neon Museum of Philadelphia (founded by Len Davidson, Philadelphia, 1985). These museums restore and display historical signage that was originally designed as advertising, in addition to presenting exhibits of neon art. Several books of photographs have also been published to draw attention to neon lighting as art. In 1994, Christian Schiess has published an anthology of photographs and interviews devoted to fifteen "light artists".
Neon signs are made using electrified, luminous tube lights that contain rarefied neon or other gases. They are the most common use for neon lighting, which was first demonstrated in a modern form in December, 1910 by Georges Claude at the Paris Motor Show. While they are used worldwide, neon signs were extremely popular in the United States from about 1920–1960. The installations in Times Square were famed, and there were nearly 2000 small shops producing neon signs by 1940. In addition to signage, neon lighting is now used frequently by artists and architects, and (in a modified form) in plasma display panels and televisions. The signage industry has declined in the past several decades, and cities are now concerned with preserving and restoring their antique neon signs (see Further reading below).
The neon sign is an evolution of the earlier Geissler tube, which is an electrified glass tube containing a "rarefied" gas (the gas pressure in the tube is well below atmospheric pressure). When a voltage is applied to electrodes inserted through the glass, an electrical glow discharge results. Geissler tubes were quite popular in the late 1800s, and the different colors they emitted were characteristics of the gases within. They were, however, unsuitable for general lighting; the pressure of the gas inside typically declined in use. The direct predecessor of neon tube lighting was the Moore tube, which used nitrogen or carbon dioxide as the luminous gas and a patented mechanism for maintaining pressure; Moore tubes were sold for commercial lighting for a number of years in the early 1900s.
The discovery of neon in 1898 included the observation of a brilliant red glow in Geissler tubes. Immediately following neon's discovery, neon tubes were used as scientific instruments and novelties. A sign created by Perley G. Nutting and displaying the word "neon" may have been shown at the Louisiana Purchase Exposition of 1904, although this claim has been disputed; in any event, the scarcity of neon would have precluded the development of a lighting product. However, after 1902, Georges Claude's company in France, Air Liquide, began producing industrial quantities of neon, essentially as a byproduct of their air liquefaction business. From December 3-18, 1910, Claude demonstrated two 12-metre (39 ft) long bright red neon tubes at the Paris Motor Show. This demonstration lit a peristyle of the Grand Palais (a large exhibition hall). Claude's associate, Jacques Fonseque, realized the possibilities for a business based on signage and advertising. By 1913 a large sign for the vermouth Cinzano illuminated the night sky in Paris, and by 1919 the entrance to the Paris Opera was adorned with neon tube lighting. Over the next several years, patents were granted to Claude for two innovations still used today: a "bombardment" technique to remove impurities from the working gas of a sealed sign, and a design for the internal electrodes of the sign that prevented their degradation by sputtering.
In 1923, Georges Claude and his French company Claude Neon introduced neon gas signs to the United States by selling two to a Packard car dealership in Los Angeles. Earle C. Anthony purchased the two signs reading "Packard" for $1,250 apiece. Neon lighting quickly became a popular fixture in outdoor advertising. Visible even in daylight, people would stop and stare at the first neon signs for hours, dubbed "liquid fire."
The next major technological innovation in neon lighting and signs was the development of fluorescent tube coatings. Jacques Risler received a French patent in 1926 for these. Neon signs that use an argon/mercury gas mixture emit a good deal of ultraviolet light. When this light is absorbed by a fluorescent coating, preferably inside the tube, the coating (called a "phosphor") glows with its own color. While only a few colors were initially available to sign designers, after the Second World War (1939-1945) phosphor materials were researched intensively for use in color televisions. About two dozen colors were available to neon sign designers in the 1960s, and today there are nearly 100 available colors.
Neon tube signs are produced by the craft of bending glass tubing into shapes. A worker skilled in this craft is known as a glass bender, neon bender or tube bender. The neon tube is made out of 3-4' straight sticks of hollow glass sold by sign suppliers to neon shops worldwide, where they are manually assembled into individual custom designed and fabricated lamps. There are many dozens of colors available, determined by the type of glass tubing and the composition of the gas filling.
Neon sign manufacturing is a cottage industry and an eclectic art, and in most cases, is organized as a small family business. Even today, almost all neon tubes are hand made and labor intensive. The shop equipment used to fabricate signs is itself typically custom assembled from scratch from discrete parts by the craftsmen who will use the equipment.
Tubing in external diameters ranging from about 8–15 mm with a 1 mm wall thickness is most commonly used, although 6mm tubing is now commercially available in colored glass tubes. The tube is heated in sections using several types of burners that are selected according to the amount of glass to be heated for each bend. These burners include ribbon, cannon, or crossfires, as well as a variety of gas torches. Ribbon burners are strips of fire that make the gradual bends while crossfires, when used, make the sharp bends.
The interior of the tubes may be coated with a thin phosphorescent powder coating, affixed to the interior wall of the tube by a binding material. The tube is filled with a purified gas mixture, and the gas ionized by a high voltage applied between the ends of the sealed tube through cold cathodes welded onto the ends. The color of the light emitted by the tube may be just that coming from the gas, or the light from the phosphor layer. Different phosphor-coated tubing sections may be butt welded together using glass working torches to form a single tube of varying colors, for effects such as a sign where each letter displays a different color letter within a single word, such as shown in the sign in the photo above right.
"Neon" is used to denote the general type of lamp, but neon gas is only one of the types of tube gases principally used in commercial application. Pure neon gas is used to produce only about a third of the colors. The greatest number of colors is produced by filling with another inert gas, argon, and a drop of mercury (Hg) which is added to the tube immediately after purification. When the tube is ionized by electrification, the mercury evaporates into mercury vapor, which fills the tube and produces strong ultraviolet light. The ultraviolet light thus produced excites the various phosphor coatings designed to produce different colors. Even though this class of neon tubes use no neon at all, they are still denoted as "neon." Mercury-bearing lamps are a type of cold-cathode fluorescent lamps.
Each type of neon tubing produces two completely different possible colors, one with neon gas and the other with argon/mercury. Some "neon" tubes are made without phosphor coatings for some of the colors. Clear tubing filled with neon gas produces the ubiquitous yellowish orange color with the interior plasma column clearly visible, and is the cheapest and simplest tube to make. Traditional neon glasses in America over 20 years old are lead glass that are easy to soften in gas fires, but recent environmental and health concerns of the workers has prompted manufacturers to seek more environmentally safe special soft glass formulas. One of the vexing problems avoided this way is lead glass' tendency to burn into a black spot emitting lead fumes in a bending flame too rich in the fuel/oxygen mixture. Another traditional line of glasses was colored soda lime glasses coming in a myriad of glass color choices, which produce the highest quality, most hypnotically vibrant and saturated hues. Still more color choices are afforded in either coating, or not coating, these colored glasses with the various available exotic phosphors.
It is the wide range of colors and the ability to make a tube that can last for years if not decades without replacement, that makes this an art. Since these tubes require so much custom labor, they would have very little economic viability if they did not have such a long lifetime when well processed. The intensity of neon light produced increases slowly as the tube diameter grows smaller, that is, the intensity varies inversely with the square root of the interior diameter of the tubing, and the resistance of the tube increases as the tubing diameter decreases accordingly, because tube ionization is greatest at the center of the tube, and the ions migrate to and are recaptured and neutralized at the tube walls. The greatest cause of neon tube failure is the gradual absorption of neon gas by high voltage ion implantation into the interior glass walls of the tubes which depletes the gas, and eventually causes the tube resistance to rise to a level that it can no longer light at the rated voltage, but this may take 7–10 years.
The actual cause of 80% of neon sign failures is the burnout of the high voltage electrical wires connecting the tubes inside of metal conduits. A very common type of neon sign is made from a formed metal box having a colored translucent face, called "channel lettering". Newer channel letter signs are being replaced by high brightness LEDs.
This long lifetime has created a practical market for neon use for interior architectural cove lighting in a wide variety of uses including homes, where the tube can be bent to any shape, fitted in a small space, and can do so without requiring tube replacement for a decade or more.
A section of the glass is heated until it is malleable; then it is bent into shape and aligned to a pattern containing the graphics or lettering that the final product will ultimately conform to. This is where the real art of neon comes in that takes some artisans from a year up to several years of practice to master. A tube bender corks off the hollow tube before heating and holds a latex rubber blow hose at the other end, through which he gently presses a small amount of air in order to keep the tube diameter constant as it is bending. The trick of bending is to bend one small section or bend at a time, heating one part of the tubing so that it is soft, without heating some other part of the tube as well, which would make the bend uncontrollable. A bend, once the glass is heated, must be brought to the pattern and fitted rapidly before the glass hardens again because it is difficult to reheat once completely cooled without risking breakage. It is frequently necessary to skip one or more bends and come back to it later, by measuring carefully along the length of the tube. One tube letter may contain 7-10 small bends, and mistakes are not easily corrected without going back and starting all over again. If more tubing is required, another piece is welded onto it, or the parts can be all welded onto each other at the final step. The finished tube must be absolutely vacuum tight in order to operate, and it must be vacuum clean inside. Once the tube is filled with mercury, if any mistake is made after that, the entire tube had, or should, be started over again, because breathing heated mercury impregnated glass and phosphor causes long term heavy metal poisoning in neon workers. Sticks of tubing are joined until the tube reaches an impractical size, and several tubes are joined in series with the high voltage neon transformer. Extreme ends of the electrical circuit must be isolated from each other to prevent tube puncture and buzzing from corona effect.
A cold cathode electrode is melted (or welded) to each end of the tube as it is finished. The electrodes are also traditionally lead glass and contain a small metal shell with two wires protruding through the glass to which the sign wiring will later be attached. All welds and seals must be perfectly leak-proof to high vacuum before proceeding further.
The tube is attached to a manifold which is itself attached to a high-quality vacuum pump. The tube is then evacuated of air until it reaches near-vacuum. During evacuation, a high current is forced through the tube via the wires protruding from each electrode (in a process known as "bombarding"). This current and voltage is far above the level that occurs in final operation of the tube. The current depends on the specific electrodes used and the diameter of the tube, but is typically in the 450 mA to 800 mA range, at an applied voltage usually between 22,000-26,000 V. The bombarding transformer acts as an adjustable constant current source, and the voltage produced depends on the length and pressure of the tube. Typically the operator will maintain the pressure as high as the bombarder will allow to ensure maximum power dissipation and heating.
This very high power dissipation in the tube heats the glass walls to a temperature of several hundred degrees Celsius, and any dirt and impurities within are drawn off in the gasified form by the vacuum pump. The greatest impurities that are driven off this way are the gases that coat the inside wall of the tubing by adsorption, mainly oxygen, carbon dioxide, and especially water vapor. The current also heats the electrode metal to over 600oC, producing a bright orange incandescent color. The cathodes are prefabricated hollow metal shells with a small opening (sometimes a ceramic donut aperture) which contains in the interior surface of the shell a light dusting of a cold cathode low work function powder (usually a powder ceramic molar eutectic point mixture including BaCO2, combined with other alkaline earth oxides, which reduces to BaO2 when heated to about 500 degrees F, and reduces the work function of the electrode for cathodic emission. Barium Oxide has a work function of roughly 2 whereas tungsten at room temperature has a work function exponentially 100 times more, or 4.0. This represents the cathode drop or electron energy required to remove electrons from the surface of the cathode. This avoids the necessity of using a hot wire thermoelectric cathode such as is used in conventional fluorescent lamps. And for that reason, neon tubes are extremely long lived when properly processed, in contrast to fluorescent tubing, because there is no wire filament as there is in a fluorsecent tube to burn out like a common light bulb. The principal purpose of doing this is to purify the interior of the tube before the tube is sealed off so that when it is operated, these gases and impurities are not driven off and released by the plasma and the heat generated into the sealed tube, which would quickly burn the metal cathodes and mercury droplets (if pumped with argon/mercury) and oxidize the interior gases and cause immediate tube failure. The more thorough the purification of the tube is, the longer lasting and stable the tube will be in actual operation. Once these gases and impurities are liberated under pre-filling bombardment into the tube interior they are quickly evacuated by the pump.
While still attached to the manifold, the tube is allowed to cool while pumping down to the lowest pressure the system can achieve. It is then filled to a low pressure of a few torrs (millimeters of mercury) with one of the noble gases, or a mixture of them, and sometimes a small amount of mercury. This gas fill pressure represents roughly 1/100th of the pressure of the atmosphere. The required pressure depends on the gas used and the diameter of the tube, with optimal values ranging from 6 Torr (0.8 kPa) (for a long 20 mm tube filled with argon/mercury) to 27 Torr (3.6 kPa) (for a short 8 mm diameter tube filled with pure neon). Neon or argon are the most common gases used; krypton, xenon, and helium are used by artists for special purposes but are not used alone in normal signs. A premixed combination of argon and helium is often used in lieu of pure argon when a tube is to be installed in a cold climate, since the helium increases voltage drop (and thus power dissipation), warming the tube to operating temperature faster. Neon glows bright red or reddish orange when lit. When argon or argon/helium is used, a tiny droplet of mercury is added. Argon by itself is very dim pale lavender when lit, but the droplet of mercury fills the tube with mercury vapor when sealed, which then emits ultraviolet light upon electrification. This ultraviolet emission allows finished argon/mercury tubes to glow with a variety of bright colors when the tube has been coated on the interior with ultraviolet-sensitive phosphors after being bent into shape.
An alternate way of processing finished neon tubes has also been used. Because the only purpose of bombardment by electrical means is to purify the interior of tubes, it is also possible to produce a tube by heating the tube externally either with a torch or with an oven, while heating the electrode with a Radio Frequency Induction Heating coil (RFIH). While this is less productive, it creates a cleaner custom tube with significantly less cathode damage, longer life and brilliance, and can produce tubes of very small sizes and diameters, down to 6mm OD. The tube is heated thoroughly under high vacuum without external electrical application, until the outgassed gases can be seen to have been totally depleted and the pressure drops to a high vacuum again. Then the tube is filled, sealed and the mercury dropped and shaken.
The finished glass pieces are illuminated by either a neon sign transformer or a switching power supply running at voltages ranging between 3-15 kV and currents between 20 and 120 mA. These power supplies operate as constant-current sources (a high voltage supply with a very high internal impedance), since the tube has a negative characteristic electrical impedance. Standard tube tables established in the early days of neon are still used that specify the gas fill pressures, in either Ne or Hg/Ar, as a function of tube length in feet, tube diameter and transformer voltage.
The standard traditional neon transformer, a magnetic shunt transformer, is a special non-linear type designed to keep the voltage across the tube raised to whatever level is necessary to produce the fixed current needed, up to the maximum limit of the neon footage possible.
Newer, compact high frequency inverter-converter transformers developed in the early '90s are used as well, especially when low Radio Frequency Interference (RFI) is needed, such as in locations near high-fidelity sound equipment. The reason for this is that at 20 kHz, the typical frequency of these solid state transformers, the plasma electron-ion recombination time is too short to extinguish and reignite the plasma in the tube at every 1/120th second as in 50/60Hz transformers and so the plasma does not broadcast high frequency switching noise. The plasma simply remains lit at all times, becoming radio noise free.
The most common current rating is 30 mA for general use, with 60 mA used for high-brightness applications like channel letters or architectural lighting. 120 mA sources are occasionally seen in illuminating applications, but are uncommon since special electrodes are required to withstand the current, and an accidental shock from a 120 mA transformer is much more likely to be fatal than from the lower current supplies.
The efficiency of neon lighting ranges between that of ordinary incandescent lights and that of fluorescent lamps, depending on color. On a per-watt basis, incandescents produce 10 to 20 lumens, while fluorescents produce 50 to 100 lumens. Neon light efficiency ranges from 10 lumens per watt for red, up to 60 lumens for green and blue when these colors result from internal phosphor coatings.
A trick of the eye is used to produce visually distinct neon display segments by blocking out parts of the tube with an opaque coating. One complete assembly may be composed of contiguous tube elements joined by glass welding to one another so that the same current passes through, for example, several letters joined end to end from cathode to cathode. To the untrained eye, this looks like separate tubes, but the electrical splice is the plasma inside the crossover glass itself. The entire tube lights up, but the segments that the viewer is not supposed to see are covered with highly opaque special black or gray glass paint. This heat-resistant coating is either painted on or dipped. Without blockout paint, the unintended visual connections would make the display appear confusing.
In most mass produced low-priced signs today, clear glass tubing is coated with translucent paint to produce colored light. In this way, several different colors can be produced inexpensively from a single glowing tube. Over time, elevated temperatures, thermal cycling, or exposure to weather may cause the colored coating to flake off the glass or change its hue. A more expensive alternative is to use high-quality colored glass tubing, which retains a more stable appearance as it ages.
The light-emitting tubes form colored lines with which a text can be written or a picture drawn, including various decorations, especially in advertising and commercial signage. By programming sequences of switching parts on and off, there are many possibilities for dynamic light patterns that form animated images.
Neon signs are increasingly replaced with LED signs due to the lower cost and longer operating life of LEDs. This trend seems likely to increase given the steady advance in LED luminosity and decreasing cost of high-intensity LEDs.
Argon (with mercury)
Neon lights as commercial advertising designed & fabricated by neon glass artist Eileen Thompkins, Owner of Empress Signs LLC.
A deteriorated, 1950s era sign typical of Googie architecture; "Ships" was a chain of coffee shops in Los Angeles.
Original Whitey's Restaurant "EAT" sign in Arlington, VA
An organic light emitting diode (OLED) is a light-emitting diode (LED) in which the emissive electroluminescent layer is a film of organic compounds which emit light in response to an electric current. This layer of organic semiconductor material is situated between two electrodes. Generally, at least one of these electrodes is transparent.
OLEDs are used in television screens, computer monitors, small, portable system screens such as mobile phones and PDAs, watches, advertising, information, and indication. OLEDs are also used in light sources for space illumination and in large-area light-emitting elements. Due to their early stage of development, they typically emit less light per unit area than inorganic solid-state based LED point-light sources.
An OLED display functions without a backlight. Thus, it can display deep black levels and can be thinner and lighter than liquid crystal displays. In low ambient light conditions such as dark rooms, an OLED screen can achieve a higher contrast ratio than an LCD using either cold cathode fluorescent lamps or the more recently developed LED backlight.
There are two main families of OLEDs: those based upon small molecules and those employing polymers. Adding mobile ions to an OLED creates a Light-emitting Electrochemical Cell or LEC, which has a slightly different mode of operation.
OLED displays can use either passive-matrix (PMOLED) or active-matrix addressing schemes. Active-matrix OLEDs (AMOLED) require a thin-film transistor backplane to switch each individual pixel on or off, and can make higher resolution and larger size displays possible.
The first observations of electroluminescence in organic materials were in the early 1950s by A. Bernanose and co-workers at the Nancy-Université, France. They applied high-voltage alternating current (AC) fields in air to materials such as acridine orange, either deposited on or dissolved in cellulose or cellophane thin films. The proposed mechanism was either direct excitation of the dye molecules or excitation of electrons.
In 1960, Martin Pope and co-workers at New York University developed ohmic dark-injecting electrode contacts to organic crystals. They further described the necessary energetic requirements (work functions) for hole and electron injecting electrode contacts. These contacts are the basis of charge injection in all modern OLED devices. Pope's group also first observed direct current (DC) electroluminescence under vacuum on a pure single crystal of anthracene and on anthracene crystals doped with tetracene in 1963 using a small area silver electrode at 400V. The proposed mechanism was field-accelerated electron excitation of molecular fluorescence.
Pope's group reported in 1965 that in the absence of an external electric field, the electroluminescence in anthracene crystals is caused by the recombination of a thermalized electron and hole, and that the conducting level of anthracene is higher in energy than the exciton energy level. Also in 1965, W. Helfrich and W. G. Schneider of the National Research Council in Canada produced double injection recombination electroluminescence for the first time in an anthracene single crystal using hole and electron injecting electrodes, the forerunner of modern double injection devices. In the same year, Dow Chemical researchers patented a method of preparing electroluminescent cells using high voltage (500–1500 V) AC-driven (100–3000 Hz) electrically-insulated one millimetre thin layers of a melted phosphor consisting of ground anthracene powder, tetracene, and graphite powder. Their proposed mechanism involved electronic excitation at the contacts between the graphite particles and the anthracene molecules.
Device performance was limited by the poor electrical conductivity of contemporary organic materials. This was overcome by the discovery and development of highly conductive polymers. For more on the history of such materials, see conductive polymers.
Electroluminescence from polymer films was first observed by Roger Partridge at the National Physical Laboratory in the United Kingdom. The device consisted of a film of poly(n-vinylcarbazole) up to 2.2 micrometres thick located between two charge injecting electrodes. The results of the project were patented in 1975 and published in 1983.
The first diode device was reported at Eastman Kodak by Ching W. Tang and Steven Van Slyke in 1987. This device used a novel two-layer structure with separate hole transporting and electron transporting layers such that recombination and light emission occurred in the middle of the organic layer. This resulted in a reduction in operating voltage and improvements in efficiency and led to the current era of OLED research and device production.
Research into polymer electroluminescence culminated in 1990 with J. H. Burroughes et al. at the Cavendish Laboratory in Cambridge reporting a high efficiency green light-emitting polymer based device using 100 nm thick films of poly(p-phenylene vinylene).
A typical OLED is composed of a layer of organic materials situated between two electrodes, the anode and cathode, all deposited on a substrate. The organic molecules are electrically conductive as a result of delocalization of pi electrons caused by conjugation over all or part of the molecule. These materials have conductivity levels ranging from insulators to conductors, and therefore are considered organic semiconductors. The highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO) of organic semiconductors are analogous to the valence and conduction bands of inorganic semiconductors.
Originally, the most basic polymer OLEDs consisted of a single organic layer. One example was the first light-emitting device synthesised by J. H. Burroughes et al., which involved a single layer of poly(p-phenylene vinylene). However multilayer OLEDs can be fabricated with two or more layers in order to improve device efficiency. As well as conductive properties, different materials may be chosen to aid charge injection at electrodes by providing a more gradual electronic profile, or block a charge from reaching the opposite electrode and being wasted. Many modern OLEDs incorporate a simple bilayer structure, consisting of a conductive layer and an emissive layer. More recent developments in OLED architecture improves quantum efficiency (up to 19%) by using a graded heterojunction. In the graded heterojunction architecture, the composition of hole and electron-transport materials varies continuously within the emissive layer with a dopant emitter. The graded heterojunction architecture combines the benefits of both conventional architectures by improving charge injection while simultaneously balancing charge transport within the emissive region.
During operation, a voltage is applied across the OLED such that the anode is positive with respect to the cathode. A current of electrons flows through the device from cathode to anode, as electrons are injected into the LUMO of the organic layer at the cathode and withdrawn from the HOMO at the anode. This latter process may also be described as the injection of electron holes into the HOMO. Electrostatic forces bring the electrons and the holes towards each other and they recombine forming an exciton, a bound state of the electron and hole. This happens closer to the emissive layer, because in organic semiconductors holes are generally more mobile than electrons. The decay of this excited state results in a relaxation of the energy levels of the electron, accompanied by emission of radiation whose frequency is in the visible region. The frequency of this radiation depends on the band gap of the material, in this case the difference in energy between the HOMO and LUMO.
As electrons and holes are fermions with half integer spin, an exciton may either be in a singlet state or a triplet state depending on how the spins of the electron and hole have been combined. Statistically three triplet excitons will be formed for each singlet exciton. Decay from triplet states (phosphorescence) is spin forbidden, increasing the timescale of the transition and limiting the internal efficiency of fluorescent devices. Phosphorescent organic light-emitting diodes make use of spin–orbit interactions to facilitate intersystem crossing between singlet and triplet states, thus obtaining emission from both singlet and triplet states and improving the internal efficiency.
Indium tin oxide (ITO) is commonly used as the anode material. It is transparent to visible light and has a high work function which promotes injection of holes into the HOMO level of the organic layer. A typical conductive layer may consist of PEDOT:PSS as the HOMO level of this material generally lies between the workfunction of ITO and the HOMO of other commonly used polymers, reducing the energy barriers for hole injection. Metals such as barium and calcium are often used for the cathode as they have low work functions which promote injection of electrons into the LUMO of the organic layer. Such metals are reactive, so require a capping layer of aluminium to avoid degradation.
Single carrier devices are typically used to study the kinetics and charge transport mechanisms of an organic material and can be useful when trying to study energy transfer processes. As current through the device is composed of only one type of charge carrier, either electrons or holes, recombination does not occur and no light is emitted. For example, electron only devices can be obtained by replacing ITO with a lower work function metal which increases the energy barrier of hole injection. Similarly, hole only devices can be made by using a cathode comprised solely of aluminium, resulting in an energy barrier too large for efficient electron injection.
Efficient OLEDs using small molecules were first developed by Dr. Ching W. Tang et al. at Eastman Kodak. The term OLED traditionally refers specifically to this type of device, though the term SM-OLED is also in use.
Molecules commonly used in OLEDs include organometallic chelates (for example Alq3, used in the organic light-emitting device reported by Tang et al.), fluorescent and phosphorescent dyes and conjugated dendrimers. A number of materials are used for their charge transport properties, for example triphenylamine and derivatives are commonly used as materials for hole transport layers. Fluorescent dyes can be chosen to obtain light emission at different wavelengths, and compounds such as perylene, rubrene and quinacridone derivatives are often used. Alq3 has been used as a green emitter, electron transport material and as a host for yellow and red emitting dyes.
The production of small molecule devices and displays usually involves thermal evaporation in a vacuum. This makes the production process more expensive and of limited use for large-area devices than other processing techniques. However, contrary to polymer-based devices, the vacuum deposition process enables the formation of well controlled, homogeneous films, and the construction of very complex multi-layer structures. This high flexibility in layer design, enabling distinct charge transport and charge blocking layers to be formed, is the main reason for the high efficiencies of the small molecule OLEDs.
Coherent emission from a laser dye-doped tandem SM-OLED device, excited in the pulsed regime, has been demonstrated. The emission is nearly diffraction limited with a spectral width similar to that of broadband dye lasers.
Polymer light-emitting diodes (PLED), also light-emitting polymers (LEP), involve an electroluminescent conductive polymer that emits light when connected to an external voltage. They are used as a thin film for full-spectrum colour displays. Polymer OLEDs are quite efficient and require a relatively small amount of power for the amount of light produced.
Vacuum deposition is not a suitable method for forming thin films of polymers. However, polymers can be processed in solution, and spin coating is a common method of depositing thin polymer films. This method is more suited to forming large-area films than thermal evaporation. No vacuum is required, and the emissive materials can also be applied on the substrate by a technique derived from commercial inkjet printing. However, as the application of subsequent layers tends to dissolve those already present, formation of multilayer structures is difficult with these methods. The metal cathode may still need to be deposited by thermal evaporation in vacuum.
Typical polymers used in PLED displays include derivatives of poly(p-phenylene vinylene) and polyfluorene. Substitution of side chains onto the polymer backbone may determine the colour of emitted light or the stability and solubility of the polymer for performance and ease of processing.
While unsubstituted poly(p-phenylene vinylene) (PPV) is typically insoluble, a number of PPVs and related poly(naphthalene vinylene)s (PNVs) that are soluble in organic solvents or water have been prepared via ring opening metathesis polymerization.
Phosphorescent organic light emitting diodes use the principle of electrophosphorescence to convert electrical energy in an OLED into light in a highly efficient manner, with the internal quantum efficiencies of such devices approaching 100%.
Typically, a polymer such as poly(n-vinylcarbazole) is used as a host material to which an organometallic complex is added as a dopant. Iridium complexes such as Ir(mppy)3 are currently the focus of research, although complexes based on other heavy metals such as platinum have also been used.
The heavy metal atom at the centre of these complexes exhibits strong spin-orbit coupling, facilitating intersystem crossing between singlet and triplet states. By using these phosphorescent materials, both singlet and triplet excitons will be able to decay radiatively, hence improving the internal quantum efficiency of the device compared to a standard PLED where only the singlet states will contribute to emission of light.
Applications of OLEDs in solid state lighting require the achievement of high brightness with good CIE coordinates (for white emission). The use of macromolecular species like polyhedral oligomeric silsesquioxanes (POSS) in conjunction with the use of phosphorescent species such as Ir for printed OLEDs have exhibited brightnesses as high as 10,000 cd/m2.
Patternable organic light-emitting devices use a light or heat activated electroactive layer. A latent material (PEDOT-TMA) is included in this layer that, upon activation, becomes highly efficient as a hole injection layer. Using this process, light-emitting devices with arbitrary patterns can be prepared.
Colour patterning can be accomplished by means of laser, such as radiation-induced sublimation transfer (RIST).
Organic vapour jet printing (OVJP) uses an inert carrier gas, such as argon or nitrogen, to transport evaporated organic molecules (as in Organic Vapor Phase Deposition). The gas is expelled through a micron sized nozzle or nozzle array close to the substrate as it is being translated. This allows printing arbitrary multilayer patterns without the use of solvents.
Conventional OLED displays are formed by vapor thermal evaporation (VTE) and are patterned by shadow-mask. A mechanical mask has openings allowing the vapor to pass only on the desired location.
For a high resolution display like a TV, a TFT backplane is necessary to drive the pixels correctly. Currently, Low Temperature Polycrystalline silicon LTPS-TFT is used for commercial AMOLED displays. LTPS-TFT has variation of the performance in a display, so various compensation circuits have been reported. Due to the size limitation of the excimer laser used for LTPS, the AMOLED size was limited. To cope with the hurdle related to the panel size, amorphous-silicon/microcrystalline-silicon backplanes have been reported with large display prototype demonstrations.
The different manufacturing process of OLEDs lends itself to several advantages over flat-panel displays made with LCD technology.
OLED technology is used in commercial applications such as displays for mobile phones and portable digital media players, car radios and digital cameras among others. Such portable applications favor the high light output of OLEDs for readability in sunlight and their low power drain. Portable displays are also used intermittently, so the lower lifespan of organic displays is less of an issue. Prototypes have been made of flexible and rollable displays which use OLEDs' unique characteristics. Applications in flexible signs and lighting are also being developed. Philips Lighting have made OLED lighting samples under the brand name 'Lumiblade' available online.
OLEDs have been used in most Motorola and Samsung colour cell phones, as well as some HTC, LG and Sony Ericsson models. Nokia has also recently introduced some OLED products including the N85 and the N86 8MP, both of which feature an AMOLED display. OLED technology can also be found in digital media players such as the Creative ZEN V, the iriver clix, the Zune HD and the Sony Walkman X Series.
The Google and HTC Nexus One smartphone includes an AMOLED screen, as does HTC's own Desire and Legend phones. However due to supply shortages of the Samsung-produced displays, certain HTC models will use Sony's SLCD displays in the future, while the Google and Samsung Nexus S smartphone will use "Super Clear LCD" instead in some countries.
Other manufacturers of OLED panels include Anwell Technologies Limited, Chi Mei Corporation, LG, and others.
DuPont stated in a press release in May 2010 that they can produce a 50-inch OLED TV in two minutes with a new printing technology. If this can be scaled up in terms of manufacturing, then the total cost of OLED TVs would be greatly reduced. Dupont also states that OLED TVs made with this less expensive technology can last up to 15 years if left on for a normal eight hour day.
The use of OLEDs may be subject to patents held by Eastman Kodak, DuPont, General Electric, Royal Philips Electronics, numerous universities and others. There are by now literally thousands of patents associated with OLEDs, both from larger corporations and smaller technology companies .
By 2004 Samsung, South Korea's largest conglomerate, was the world's largest OLED manufacturer, producing 40% of the OLED displays made in the world, and as of 2010 has a 98% share of the global AMOLED market. The company is leading the world OLED industry, generating $100.2 million out of the total $475 million revenues in the global OLED market in 2006. As of 2006, it held more than 600 American patents and more than 2800 international patents, making it the largest owner of AMOLED technology patents.
Samsung SDI announced in 2005 the world's largest OLED TV at the time, at 21 inches (53 cm). This OLED featured the highest resolution at the time, of 6.22 million pixels. In addition, the company adopted active matrix based technology for its low power consumption and high-resolution qualities. This was exceeded in January 2008, when Samsung showcased the world's largest and thinnest OLED TV at the time, at 31 inches and 4.3 mm.
In May 2008, Samsung unveiled an ultra-thin 12.1 inch laptop OLED display concept, with a 1,280×768 resolution with infinite contrast ratio. According to Woo Jong Lee, Vice President of the Mobile Display Marketing Team at Samsung SDI, the company expected OLED displays to be used in notebook PCs as soon as 2010.
In October 2008, Samsung showcased the world's thinnest OLED display, also the first to be 'flappable' and bendable. It measures just 0.05 mm (thinner than paper), yet a Samsung staff member said that it is "technically possible to make the panel thinner". To achieve this thickness, Samsung etched an OLED panel that uses a normal glass substrate. The drive circuit was formed by low-temperature polysilicon TFTs. Also, low-molecular organic EL materials were employed. The pixel count of the display is 480 × 272. The contrast ratio is 100,000:1, and the luminance is 200 cd/m². The colour reproduction range is 100% of the NTSC standard.
In the same month, Samsung unveiled what was then the world's largest OLED Television at 40-inch with a Full HD resolution of 1920×1080 pixel. In the FPD International, Samsung stated that its 40-inch OLED Panel is the largest size currently possible. The panel has a contrast ratio of 1,000,000:1, a colour gamut of 107% NTSC, and a luminance of 200 cd/m² (peak luminance of 600 cd/m²).
At the Consumer Electronics Show (CES) in January 2010, Samsung demonstrated a laptop computer with a large, transparent OLED display featuring up to 40% transparency and an animated OLED display in a photo ID card.
Samsung's latest AMOLED smartphones use their Super AMOLED trademark, with the Samsung Wave S8500 and Samsung i9000 Galaxy S being launched in June 2010. In January 2011 Samsung announced their Super AMOLED Plus displays - which offer several advances over the older Super AMOLED displays - real stripe matrix (50% more sub pixels), thinner form factor, brighter image and a 18% reduction in energy consumption.
The Sony CLIÉ PEG-VZ90 was released in 2004, being the first PDA to feature an OLED screen. Other Sony products to feature OLED screens include the MZ-RH1 portable minidisc recorder, released in 2006 and the Walkman X Series.
At the Las Vegas CES 2007, Sony showcased 11-inch (28 cm, resolution 960×540) and 27-inch (68.5 cm, full HD resolution at 1920×1080) OLED TV models. Both claimed 1,000,000:1 contrast ratios and total thicknesses (including bezels) of 5 mm. In April 2007, Sony announced it would manufacture 1000 11-inch OLED TVs per month for market testing purposes. On October 1, 2007, Sony announced that the 11-inch model, now called the XEL-1, would be released commercially; the XEL-1 was first released in Japan in December 2007.
In May 2007, Sony publicly unveiled a video of a 2.5-inch flexible OLED screen which is only 0.3 millimeters thick. At the Display 2008 exhibition, Sony demonstrated a 0.2 mm thick 3.5 inch display with a resolution of 320×200 pixels and a 0.3 mm thick 11 inch display with 960×540 pixels resolution, one-tenth the thickness of the XEL-1.
In July 2008, a Japanese government body said it would fund a joint project of leading firms, which is to develop a key technology to produce large, energy-saving organic displays. The project involves one laboratory and 10 companies including Sony Corp. NEDO said the project was aimed at developing a core technology to mass-produce 40 inch or larger OLED displays in the late 2010s.
In October 2008, Sony published results of research it carried out with the Max Planck Institute over the possibility of mass-market bending displays, which could replace rigid LCDs and plasma screens. Eventually, bendable, transparent OLED screens could be stacked to produce 3D images with much greater contrast ratios and viewing angles than existing products.
Sony exhibited a 24.5" prototype OLED 3D television during the Consumer Electronics Show in January 2010.
In January 2011, Sony announced the PlayStation Vita handheld game console (the successor to the PSP) will feature a 5-inch OLED screen.
On February 17, 2011, Sony announced its 25" OLED Professional Reference Monitor aimed at the Cinema and high end Drama Post Production market.
As of 2010, LG produces one model of OLED television, the 15 inch 15EL9500 and has announced a 31" OLED 3D television for March 2011 (however as of June 2011, the 31" product is still not available). LG plans a 55 inch prototype for 2012.
The sulfur lamp (also sulphur lamp) is a highly efficient full-spectrum electrodeless lighting system whose light is generated by sulfur plasma that has been excited by microwave radiation. The technology was developed in the early 1990s, but, although it appeared initially to be very promising, sulfur lighting was a commercial failure by the late 1990s. Since 2005, lamps are again being manufactured for commercial use.
The sulfur lamp consists of a golf ball-sized (30 mm) fused-quartz bulb containing several milligrams of sulfur powder and argon gas at the end of a thin glass spindle. The bulb is enclosed in a microwave-resonant wire-mesh cage. A magnetron, much like the ones in home microwave ovens, bombards the bulb, via a waveguide, with 2.45 GHz microwaves. The microwave energy excites the gas to five atmospheres pressure, which in turn heats the sulfur to an extreme degree forming a brightly glowing plasma capable of illuminating a large area. Because the bulb heats considerably, it is necessary to provide forced air cooling to prevent it from melting. The bulb is usually placed at the focus of a parabolic reflector to direct all the light in one direction.
It would be impossible to excite the sulfur using traditional electrodes; the sulfur would quickly react with and destroy any metallic electrode. A patent pending to employ coated electrodes is discussed in Future prospects, below. The absence of electrodes allows for a much greater variety of light-generating substances to be used than those used in traditional lamps.
The design life of the bulb is approximately 60,000 hours. The design life of the magnetron has been improved by the Germany/England based Plasma International so it can also last for that same period.
The warm-up time of the sulfur lamp is notably shorter than for other gas discharge lamps, with the exception of fluorescent lamps, even at low ambient temperatures. It reaches 80% of its final luminous flux within twenty seconds, and the lamp can be restarted approximately five minutes after a power cut.
The first prototype lamps were 5.9 kW units, with a system efficiency of 80 lumens per watt. The first production models were 1.4 kW with an output of 135,000 lumens. Later models were able to eliminate the cooling fan and improve luminous efficacy to 100 lumens per watt.
The sulfur plasma consists mainly of dimer molecules (S2), which generate the light through molecular emission. Unlike atomic emission, the emission spectrum is continuous throughout the visible spectrum. As much as 73% of the emitted radiation is in the visible spectrum, with a small amount in infrared energy and less than 1% in ultraviolet light.
The spectral output peaks at 510 nanometres, imparting a greenish hue to the illuminated environment. The correlated color temperature is about 6,000 kelvins with a CRI of 79. The lamp can be dimmed to 15% without affecting the light quality.
A magenta filter can be used to give the light a warmer feel. Such a filter was used on the lamps at the National Air and Space Museum in Washington, D.C.
The addition of other chemicals in the bulb might improve color rendition. Sulfur lamp bulbs with calcium bromide (CaBr2) added produce a similar spectrum plus a spike in red wavelengths at 625 nm. Other additives such as lithium iodide (LiI) and sodium iodide (NaI) can be used to modify the output spectra.
The technology was conceived by engineer Michael Ury, physicist Charles Wood and their colleagues in 1990. With support from the United States Department of Energy, it was further developed in 1994 by Fusion Lighting of Rockville, Maryland, a spinoff of the Fusion UV division of Fusion Systems Corporation. Its origins are in microwave discharge light sources used for ultraviolet curing in the semiconductor and printing industries. The Fusion UV division was later sold to Spectris plc, and the rest of Fusion Systems was later acquired by the Eaton Corporation.
Only two production models were developed, both with similar specifications: the Solar 1000 in 1994 and the Light Drive 1000 in 1997, which was a refinement of the previous model.
Production of these lamps ended in 1998. Fusion Lighting closed its doors in early 2002, after having used up approximately $90 million in venture capital. Their patents were licensed to the LG Group. The Internet Archive has a copy of Fusion Lighting's defunct website. Their lamps were installed in more than one hundred facilities worldwide, but many of them have already been removed.
In 2001, Ningbo Youhe New Lighting Source Co., Ltd, in Ningbo, China, produced its own sulfur lamp version. The company's website is no longer online and may be out of business, but information on these lamps is available from its archived copy at the Internet Archive.
In 2006, LG Electronics began production of its sulfur lamps, called Plasma Lighting System (PLS).
The magnetrons in these lamps may cause electromagnetic interference in the 2.4 GHz wireless spectrum, which is used by Wi-Fi, cordless phones and satellite radio in North America. Fearing interference with their broadcasts, Sirius and XM satellite radio petitioned the United States Federal Communications Commission (FCC) to force Fusion Lighting to reduce the electromagnetic emissions of their lamps by 99.9%. In 2001, Fusion Lighting agreed to install metal shielding around their lamps to reduce electromagnetic emissions by 95%.
In May 2003, the FCC terminated the proceeding that would have defined out-of-band emission limits for radio-frequency lights operating at 2.45 GHz, saying the record of the proceeding had become outdated and Fusion Lighting had stopped working on such lamps. The order concluded:
We therefore decline to provide the requested relief from the Satellite Radio Licensees to prohibit operation of all RF lights in the 2.45 GHz band, as we find that the requested prohibition is overarching and is not warranted based on the circumstances. If there is evidence that any entity will seek to operate RF lights in the 2.45 GHz band and cause harmful interference to satellite radio receivers as a consequence, and our existing limits prove inadequate, we will at that time take appropriate action.
Unlike fluorescent and high-intensity discharge lamps, sulfur lamps contain no mercury. Therefore, sulfur lamps do not pose a threat to the environment nor require special disposal. In addition, use of sulfur lamps has the potential to reduce the total amount of energy required for lighting.
Because the amount of light produced from one bulb is so great, it is usually necessary to distribute the light to areas far removed from the lamp. The most common method used is light pipes.
The 3M light pipe is a long, transparent, hollow cylinder with a prismatic surface developed by 3M that distributes the light uniformly over its length. Light pipes can be as long as 40 metres (130 ft) and are assembled on site from shorter, modular units. The light pipe is attached to the parabolic reflector of the sulfur lamp. For shorter pipes, there will be a mirror at the opposite end; for longer ones, there will be a lamp at each end. The overall appearance of a light pipe has been compared to that of a giant-sized fluorescent tube. One sulfur lamp with a light pipe can replace dozens of HID lamps. In the National Air and Space Museum, three lamps, each with a 27-metre (89 ft) pipe, replaced 94 HID lamps while greatly increasing the amount of light delivered.
The greatly reduced number of lamps may simplify maintenance and reduce installation costs but may also require a backup system for areas where lighting is critical. The light pipes allow the lamp to be placed in an easily accessible area for maintenance and away from places where the heat of the lamp may be a problem.
A secondary reflector is a structure with a mirrored surface placed directly into the path of the beam of light as it exits the parabolic primary reflector of the lamp. A secondary reflector can have a complex geometry which allows it to break up the light and direct it to where it is desired. It can spotlight an object or spread out the light for general illumination.
At Sundsvall-Härnösand Airport near Sundsvall, Sweden, airfield lighting is provided by sulfur lamps mounted on towers 30 metres tall. The lamps are directed upward and shine their light onto wing-shaped secondary reflectors that spread the light out and direct it downward. In this way, one lamp can illuminate an area 30 by 80 metres (100 by 260 ft).
At the headquarters of DONG Energy, an energy company in Denmark, a single sulfur lamp directs its light onto numerous specular reflectors and diffusers to illuminate the entrance hall as well as several sculptures outside of the building.
At the entrance to University Hospital in Lund, Sweden, secondary reflectors on the ceiling are clad with highly reflective films, but shaped so as to avoid any glare. Moreover, since these films have a microprismatic surface structure that splits up the beams, the risk of glare problems is further reduced. The fact that the reflectors move the light source far away from the eye of anyone who would happen to look into them helps to further eliminate glare problems.
Indirect fixtures direct most of their luminous flux upward toward a ceiling. A highly reflective ceiling can then serve as a secondary source of diffusive, low luminance, high visual quality lighting for interior spaces. The primary advantages of indirect lighting are the opportunity to significantly reduce indirect glare potential and to completely eliminate direct source viewing.
At the Sacramento Municipal Utility District (SMUD) headquarters building, two sulfur lamps were installed in the tops of free-standing kiosks. The 4.2-metre (13 ft 9 in) high ceiling was retrofit with high reflectance (90%), white acoustic ceiling tile. The lamps direct their light upward, and it is reflected off the ceiling providing indirect light. Narrow, medium, or wide beam patterns can be created by choosing various reflector elements.
Light pipes would not be necessary in applications such as stadium lighting, where a plain fixture can be mounted high enough so that the light can spread over a large area. The installation at Hill Air Force Base contains lamps with light pipes as well as downlight fixtures mounted high in an aircraft hangar.
Optical fibers have been studied as a distribution system for sulfur lamps, but no practical system has ever been marketed.
Sulfur lamps can be used as light sources in scientific instruments.
The development of an affordable, efficient, and long-lived microwave source is a technological hurdle to cost reduction and commercial success. The lamp prototypes were only available in high wattages (1000+ W), which impeded adoption in applications where light output demands were not great. The sulfur lamp has problems with the life of the magnetron and the motor that rotates the bulb and noise from the cooling fan. Because the lamp has moving parts, reliability remains a critical issue, and system maintenance may impede market adoption.
Researchers have had some success at eliminating the need to rotate the bulb by using circularly polarized microwaves to spin the plasma discharge instead. Other experiments have used sodium iodide, scandium iodide, indium monobromide (InBr), or tellurium as the light-generating medium.
A patent #20070075617 is pending since 2006 for a sulfur lamp with electrodes — in fact, a more traditional gas–discharge lamp where a magnetron is not required. Various electrode coatings are suggested to combat high chemical activity of sulfur. As usual with patents, though, only commercial applications will reveal whether this design is viable.
Many of the installations of the lamps were for testing purposes only, but there remain a few sites where the lamps are in use as the primary lighting source. Perhaps the most visible of these would be the glass atria in the National Air and Space Museum.
An electrodeless lamp is a light source in which the power required to generate light is transferred from the outside of the lamp envelope by means of (electro)magnetic fields, in contrast with a typical electrical lamp that uses electrical connections through the lamp envelope to transfer power. There are three advantages of eliminating electrodes:
Two systems are described below—one, plasma lamps, based on the use of radio waves energizing a bulb filled with sulfur or metal halides, the other, fluorescent induction lamps, based upon conventional fluorescent lamp phosphors.
Nikola Tesla demonstrated wired and wireless transfer of power to electrodeless fluorescent and incandescent lamps in his lectures and articles in the 1890s, and subsequently patented a system of light and power distribution on those principles. In the lecture before the AIEE, May 20, 1891, titled Experiments with Alternating Currents of Very High Frequency and Their Application to Methods of Artificial Illumination  and US patent 454622, among many other references in the technical and popular press are found countless records for Tesla's priority in this field. A suit filed by Tesla against J. J. Thomson for priority on the patent was subsequently granted in Tesla's favor. The transcripts of the case languish currently in archives, awaiting processing, and eventual publishing. Noting the diagrams in Tesla's lectures and patents, a striking similarity of construction to electrodeless lamps that are available on the market currently is readily apparent. Further, a statement in 1929 by Tesla, published in The World :
Surely, my system is more important than the incandescent lamp, which is but one of the known electric illuminating devices and admittedly not the best. Although greatly improved through chemical and metallurgical advances and skill of artisans it is still inefficient, and the glaring filament emits hurtful rays responsible for millions of bald heads and spoiled eyes. In my opinion, it will soon be superseded by the electrodeless vacuum tube which I brought out thirty-eight years ago, a lamp much more economical and yielding a light of indescribable beauty and softness.
In 1967 and 1968, John Anderson of General Electric   applied for patents for electrodeless lamps. Philips introduced their QL induction lighting systems, operating at 2.65 MHz, in 1990 in Europe and in 1992 in the US. Matsushita had induction light systems available in 1992. Intersource Technologies also announced one in 1992, called the E-lamp. Operating at 13.6 MHz, it was to be available on the US market in 1993.
In 1990, Michael Ury, Charles Wood and colleagues, formulated the concept of the sulphur lamp. With support from the United States Department of Energy, it was further developed in 1994 by Fusion Lighting of Rockville, Maryland, a spinoff of the Fusion UV division of Fusion Systems Corporation. Its origins are in microwave discharge light sources used for ultraviolet curing in the semiconductor and printing industries.
Since 1994, General Electric has produced its induction lamp Genura with an integrated ballast, operating at 2.65 MHz. In 1996, Osram started selling their Endura induction light system, operating at 250 kHz. It is available in the US as the Sylvania Icetron. In 1997 PQL Lighting Introduced in the US the Superior Life Brand Induction Lighting Systems. Most induction lighting systems are rated for 100,000 hours of use before requiring absolute component replacements.
Since 2005, AMKO SOLARA in Taiwan introduced induction lamps that are capable of dimming and IP based controls. Their lamps have a range from 12 to 400 watts and operate at 250 kHz.
From 1995, the former distributors of Fusion, Jenton / Jenact, expanded on the fact that energised UV-emitting plasmas act as lossy conductors to create a number of patents with respect to electrodeless UV lamps in the sterilisation / germicidal field.
Around 2000 a system was developed that concentrated radio frequency waves into a solid dielectric waveguide made of ceramic which energized a light emitting plasma in a bulb positioned inside. This system, for the first time, permitted an extremely bright and compact electrodeless lamps. The invention has been a matter of dispute. Claimed by Frederick Espiau (then of Luxim now of Topanga Technologies), Chandrashekhar Joshi and Yian Chang, these claims were disputed by Ceravision Limited. Recently a number of the core patents were assigned to Ceravision.
In 2006 Luxim introduced a projector lamp product trade-named LIFI. The company further extended the technology with light source products in instrument, entertainment, street, area and architectural lighting applications among others throughout 2007 and 2008.
In 2009 Ceravision Limited introduced the first High Efficiency Plasma (HEP) lamp under the trade name Alvara. This lamp replaces the opaque ceramic waveguide used in earlier lamps with an optically clear quartz waveguide giving greatly increased efficiency. In previous lamps, though the burner, or bulb, was very efficient, the opaque ceramic waveguide severely obstructed the collection of light. A quartz waveguide allows all of the light from the plasma to be collected.
Plasma lamps are a family of light sources that generate light by exciting a plasma inside a closed transparent burner or bulb using radio frequency (RF) power. Typically, such lamps use a noble gas or a mixture of these gases and additional materials such as metal halides, sodium, mercury or sulfur. A waveguide is used to constrain and focus the electrical field into the plasma. In operation the gas is ionized and free electrons, accelerated by the electrical field collide with gas and metal atoms. Some electrons circling around the gas and metal atoms are excited by these collisions, bringing them to a higher energy state. When the electron falls back to its original state, it emits a photon, resulting in visible light or ultraviolet radiation depending on the fill materials.
The first plasma lamp was an ultraviolet curing lamp with a bulb filled with argon and mercury vapor developed by Fusion UV. That lamp led Fusion Systems to the development of the sulfur lamp, a bulb filled with argon and sulfur which is bombarded with microwaves through a hollow waveguide.
In the past, the reliability of the technology was limited by the magnetron used to generate the microwaves. Solid state RF generation can be used and gives long life. However, using solid state chips to generate RF is approximately fifty times more expensive currently than using a magnetron and so only appropriate for high value lighting niches. It has recently been shown by Dipolar  of Sweden to be possible to greatly extend the life of magnetrons to over 40,000 hours  making low cost plasma lamps possible. Plasma lamps are currently produced by Ceravision and Luxim and in development by Topanga Technologies.
Ceravision has introduced a combined lamp and luminaire under the trade name Alvara for use in high bay and street lighting applications. It uses an optically clear quartz waveguide with an integral burner allowing all the light from the plasma to be collected. The small source also allows the luminaire to utilize more than 90% of the available light compared with 55% for typical HID fittings. Ceravision claims the highest Luminaire Efficacy Rating (LER)  of any light fitting on the market and to have created the first High Efficiency Plasma (HEP) lamp. Ceravision uses a magnetron to generate the required RF power and claim a life of 20,000 hours.
Luxim's LIFI, or light fidelity lamp, claims 120 lumens per RF watt (ie before taking into account electrical losses). The lamp has been used in Robe lighting's ROBIN 300 Plasma Spot moving headlight. It was also used in a line of, now discontinued, Panasonic rear projection TV's.
Aside from the method of coupling energy into the mercury vapour, these lamps are very similar to conventional fluorescent lamps. Mercury vapour in the discharge vessel is electrically excited to produce short-wave ultraviolet light, which then excites the phosphors to produce visible light. While still relatively unknown to the public, these lamps have been available since 1990. The first type introduced had the shape of an incandescent light bulb. Unlike an incandescent lamp or conventional fluorescent lamps, there is no electrical connection going inside the glass bulb; the energy is transferred through the glass envelope solely by electromagnetic induction.
There are two main types of magnetic induction lamp, external inductor lamps and internal inductor lamps. The original, and still widely used form of induction lamps are the internal inductor types. A more recent development is the external inductor types which have a wider range of applications and which are available in round, rectangular and "olive" shaped form factors.
External inductor lamps are basically fluorescent lamps with electromagnets wrapped around a part of the tube. In the external inductor lamps, high frequency energy, from the electronic ballast, is sent through wires, which are wrapped in a coil around a ferrite inductor on the outside of the glass tube, creating a powerful electromagnet called an inductor. The induction coil (inductor) produces a very strong magnetic field which travels through the glass and excites the mercury atoms in the interior. The mercury atoms are provided by the amalgam (a solid form of mercury). The excited mercury atoms emit UV light and, just as in a fluorescent tube, the UV light is down-converted to visible light by the phosphor coating on the inside of the tube. The glass walls of the lamp prevent the emission of the UV light as ordinary glass blocks UV radiation at the 253.7 nm and 185 nm range.
In the internal inductor form (see diagram), a glass tube (B) protrudes bulb-wards from the bottom of the discharge vessel (A), forming a re-entrant cavity. This tube contains an antenna called a power coupler, which consists of a coil wound over a tubular ferrite core. The coil and ferrite forms the inductor which couples the energy into the lamp interior
The antenna coils receive electric power from the electronic ballast (C) that generates a high frequency. The exact frequency varies with lamp design, but popular examples include 13.6 MHz, 2.65 MHz and 250 kHz. A special resonant circuit in the ballast produces an initial high voltage on the coil to start a gas discharge; thereafter the voltage is reduced to normal running level.
The system can be seen as a type of transformer, with the power coupler (inductor) forming the primary coil and the gas discharge arc in the bulb forming the one-turn secondary coil and the load of the transformer. The ballast is connected to mains electricity, and is generally designed to operate on voltages between 100 and 277 VAC at a frequency of 50 or 60 Hz. Many ballasts are available in low voltage models so can also be connected to DC voltage sources like batteries for emergency lighting purposes of for use with renewable energy (solar & wind) powered systems.
In other conventional gas discharge lamps, the electrodes are the part with the shortest life, limiting the lamp lifespan severely. Since an induction lamp has no electrodes, it can have a very long service life. For induction lamp systems with a separate ballast, the service life can be as long as 100,000 hours, which is 11.4 years continuous operation. For induction lamps with integrated ballast, the lifespan is in the 15,000 to 50,000 hours range. Extremely high-quality electronic circuits are needed for the ballast to attain such a long service life. Such lamps are typically used in commercial or industrial applications. Typically operations and maintenance costs are significantly lower with induction lighting systems due to their industry average 100,000 hour life cycle and five to ten year warranty.
These benefits offer a considerable cost savings of between 35% and 55% in energy and maintenance costs for induction lamps compared to other types of commercial and industrial lamps which they replace.
Plasma lamps are a type of electrodeless lamp energized by radio frequency (RF) power. They are distinct from the novelty plasma lamps that were popular in the 1980s.
The electrode-less lamp was invented by Nikola Tesla after his experimentation with high-frequency currents in an evacuated glass tube for the purpose of studying high voltage phenomena. The first practical plasma lamps were the sulfur lamps manufactured by Fusion Lighting. This lamp suffered a number of practical problems and did not prosper commercially. These problems have gradually been overcome by manufacturers such as Ceravision and Luxim, and high-efficiency plasma (HEP) lamps have been introduced to the general lighting market.
Modern plasma lamps are a family of light sources that generate light by exciting a plasma inside a closed transparent burner or bulb using radio frequency (RF) power. Typically, such lamps use a noble gas or a mixture of these gases and additional materials such as metal halides, sodium, mercury or sulfur. In modern plasma lamps, a waveguide is used to constrain and focus the electrical field into the plasma. In operation, the gas is ionized, and free electrons, accelerated by the electrical field, collide with gas and metal atoms. Some atomic electrons circling around the gas and metal atoms are excited by these collisions, bringing them to a higher energy state. When the electron falls back to its original state, it emits a photon, resulting in visible light or ultraviolet radiation, depending on the fill materials.
The first commercial plasma lamp was an ultraviolet curing lamp with a bulb filled with argon and mercury vapor developed by Fusion UV. That lamp led Fusion Lighting to the development of the sulfur lamp, a bulb filled with argon and sulfur that is bombarded with microwaves through a hollow waveguide. The bulb had to be spun rapidly to prevent it burning through. Fusion Lighting did not prosper commercially, but other manufacturers, such as LG Group, continue to pursue sulfur lamps. Sulfur lamps, though relatively efficient, have had a number of problems, chiefly:
In the past, the life of the plasma lamps was limited by the magnetron used to generate the microwaves. Solid state RF chips can be used and give long lives. However, using solid-state chips to generate RF is currently an order of magnitude more expensive than using a magnetron and so only appropriate for high-value lighting niches. It has recently been shown by Dipolar  of Sweden to be possible to extend the life of magnetrons to over 40,000 hours,  making low-cost plasma lamps possible.
Around the year 2000, a system was developed that concentrated radio frequency waves into a dielectric waveguide made of ceramic, which energized light-emitting plasma in a bulb positioned inside. This system, for the first time, permitted an extremely compact yet bright electrode-less lamp. The invention has been a matter of dispute. Claimed by Frederick Espiau (then of Luxim, now of Topanga Technologies), Chandrashekhar Joshi and Yian Chang, these claims were disputed by Ceravision Limited . Recently, a number of the core patents have been assigned to Ceravision  .
The use of a high-dielectric waveguide allowed the sustaining of plasmas at much lower powers—down to 100 W in some instances. It also allowed the use of conventional gas-discharge lamp fill materials which removed the need to spin the bulb. The only issue with the ceramic waveguide was that much of the light generated by the plasma was trapped inside the opaque ceramic waveguide. In 2009, Ceravision introduced an optically clear quartz waveguide that appears to resolve this issue.
High-efficiency plasma lighting is the class of plasma lamps that have system efficiencies of 90 lumens per watt or more. Lamps in this class are potentially the most energy-efficient light source for outdoor, commercial and industrial lighting. This is due not only to their high system efficiency but also to the small light source they present enabling very high luminaire efficiency.
Luminaire Efficacy Rating (LER) is the single figure of merit the National Electrical Manufacturers Association has defined to help address problems with lighting manufacturers' efficiency claims  and is designed to allow robust comparison between lighting types. It is given by the product of luminaire efficiency (EFF) times total rated lamp output in lumens (TLL) times ballast factor (BF), divided by the input power in watts (IP):
The "system efficiency" for a High Efficiency Plasma lamp is given by the last three variables, that is, it excludes the luminaire efficiency. Though plasma lamps do not have a ballast, they have an RF power supply that fulfills the equivalent function. In electrodeless lamps, the inclusion of the electrical losses, or "ballast factor", in lumens per watt claimed can be particularly significant as conversion of electrical power to radio frequency (RF) power can be a highly inefficient process.
Many modern plasma lamps, such as those manufactured by Ceravision and Luxim, have very small light sources—far smaller than HID bulbs or fluorescent tubes—leading to much higher luminaire efficiencies also. High intensity discharge lamps have typical luminaire efficiencies of 55%, and fluorescent lamps of 70%. Plasma lamps typically have luminaire efficiencies exceeding 90%.
Companies producing or developing plasma lamps include Ceravision, Luxim, Plasma International, and Topanga Technologies.
Luxim's LIFI, or light fidelity lamp, claims 120 lumens per RF watt (i.e., before taking into account electrical losses). The lamp is used by Stray Light Optical Technologies in their commercial lighting fixtures. The lamp has been used in Robe lighting's ROBIN 300 Plasma Spot moving head light. It was also used in a line of, now discontinued, Panasonic rear projection TV.
Ceravision has introduced a combined lamp and luminaire under the trade name Alvara for use in high bay and street lighting applications. It uses an optically clear quartz waveguide with an integral burner allowing all the light from the plasma to be collected. The small source also allows the luminaire to utilize more than 90% of the available light, compared with 55% for typical high-intensity discharge fittings. Ceravision claims the highest luminaire efficacy rating of any light fitting on the market and to have created the first HEP lamp. Ceravision uses a magnetron to generate the required RF power and claims a life of 20,000 hours.
A xenon arc lamp is an artificial light source. Powered by electricity, it uses ionized xenon gas to produce a bright white light that closely mimics natural daylight.
Xenon arc lamps can be roughly divided into three categories:
Each consists of a glass or fused quartz arc tube with tungsten metal electrodes at each end. The glass tube is first evacuated and then re-filled with xenon gas. For xenon flashtubes, a third "trigger" electrode usually surrounds the exterior of the arc tube. The lamp has a lifetime of around 2000 hours.
Xenon short-arc lamps were invented in the 1940s in Germany and introduced in 1951 by Osram. First launched in the 2 kW size (XBO2001), these lamps saw a wide acceptance in movie projection, where they advantageously replaced the older carbon arc lamps. The white, continuous light generated with this arc is of daylight quality but plagued by a rather low efficiency in terms of lumens of visible light output per watt of input power. Today, almost all movie projectors in theaters employ these lamps with a rating ranging from 900 watts up to 12 kW. When used in Omnimax (Imax Dome) projection systems, the power can be as high as 15 kW in a single lamp.
All modern xenon short-arc lamps use a fused quartz envelope with thorium-doped tungsten electrodes. Fused quartz is the only economically feasible material currently available that can withstand the high pressure (25 atmospheres for an IMAX bulb) and high temperature present in an operating lamp while still being optically clear. The thorium dopant in the electrodes greatly enhances their electron emission characteristics. Because tungsten and quartz have different coefficients of thermal expansion, the tungsten electrodes are welded to strips of pure molybdenum metal or Invar alloy, which are then melted into the quartz to form the envelope seal.
Because of the very high power levels involved, large lamps are water-cooled. In those used in IMAX projectors, the electrode bodies are made from solid Invar and tipped with thoriated tungsten. An O-ring seals off the tube, so that the naked electrodes do not contact the water. In low power applications the electrodes are too cold for efficient electron emission and are not cooled; in high power applications an additional water cooling circuit for each electrode is necessary. To save costs, the water circuits are often not separated and the water needs to be highly deionized, which in turn lets the quartz or some laser media dissolve into the water.
In order to achieve maximum efficiency, the xenon gas inside short-arc lamps is maintained at an extremely high pressure (up to 30 atmospheres or 390 PSI), which poses safety concerns. If a lamp is dropped, or ruptures while in service, pieces of the lamp envelope can be thrown at high speed. To mitigate this, large xenon short-arc lamps are normally shipped in protective shields, which will contain the envelope fragments should breakage occur. Normally, the shield is removed once the lamp is installed in the lamp housing. When the lamp reaches the end of its useful life, the protective shield is put back on the lamp, and the spent lamp is then removed from the equipment and disposed of. As lamps age, the risk of failure increases, so bulbs being replaced are at the greatest risk of explosion. Because of the safety concerns, lamp manufacturers recommend the use of eye protection when handling xenon short-arc lamps. Because of the danger, some lamps, especially those used in IMAX projectors, require the use of full-body protective clothing.
Xenon short-arc lamps come in two distinct varieties: pure xenon, which contain only xenon gas; and xenon-mercury, which contain xenon gas and a small amount of mercury metal.
In a pure xenon lamp, the majority of the light is generated within a tiny, pinpoint-sized cloud of plasma situated where the electron stream leaves the face of the cathode. The light generation volume is cone-shaped, and the luminous intensity falls off exponentially moving from cathode to anode. Electrons passing through the plasma cloud strike the anode, causing it to heat. As a result, the anode in a xenon short-arc lamp either has to be much larger than the cathode or be water-cooled, to dissipate the heat. Pure xenon short-arc lamps have a "near daylight" spectrum, that is, the light output of the lamp is relatively flat over the entire colour spectrum.
Even in a high pressure lamp, there are some very strong emission lines in the near infrared, roughly in the region from 850–900 nm. This spectral region can contain about 10% of the total emitted light.
In xenon-mercury short-arc lamps, the majority of the light is generated in a tiny, pinpoint sized cloud of plasma situated at the tip of each electrode. The light generation volume is shaped like two intersecting cones, and the luminous intensity falls off exponentially moving towards the centre of the lamp. Xenon-mercury short-arc lamps have a bluish-white spectrum and extremely high UV output. These lamps are used primarily for UV curing applications, sterilizing objects, and generating ozone.
The very small size of the arc makes it possible to focus the light from the lamp with moderate precision. For this reason, xenon arc lamps of smaller sizes, down to 10 watts, are used in optics and in precision illumination for microscopes and other instruments, although in modern times they are being displaced by single mode laser diodes and white light supercontinuum lasers which can produce a truly diffraction limited spot. Larger lamps are employed in searchlights where narrow beams of light are generated, or in film production lighting where daylight simulation is required.
All xenon short-arc lamps generate significant amounts of ultraviolet radiation while in operation. Xenon has strong spectral lines in the UV bands, and these readily pass through the fused quartz lamp envelope. Unlike the borosilicate glass used in standard lamps, fused quartz does not attenuate UV radiation. The UV radiation released by a short-arc lamp can cause a secondary problem of ozone generation. The UV radiation strikes oxygen molecules in the air surrounding the lamp, causing them to ionize. Some of the ionized molecules then recombine as O3, ozone. Equipment that uses short-arc lamps as the light source must contain UV radiation and prevent ozone build-up.
Many lamps have a low-UV blocking coating on the envelope and are sold as "Ozone Free" lamps. Some lamps have envelopes made out of ultra-pure synthetic fused silica (trade name "Suprasil"), which roughly doubles the cost, but which allows them to emit useful light into the so-called vacuum UV region. These lamps are normally operated in a pure nitrogen atmosphere.
Xenon short-arc lamps also are manufactured with a ceramic body and an integral reflector. They are available in many wattages with either UV transmitting or blocking windows. The reflector options are parabolic (for collimated light) or elliptical (for focused light). They are used in a wide variety of applications such as video projectors, fiber optic illuminators, and search lights.
Xenon short-arc lamps are low-voltage, high-current, DC devices with a negative temperature coefficient. They require a high voltage pulse in the 20–50 kV range to start the lamp, and require an extremely well regulated DC power source. They are also inherently unstable, prone to phenomena such as plasma oscillation and thermal runaway. Because of these characteristics, xenon short-arc lamps require a sophisticated power supply to achieve stable, long-life operation. The usual approach is to regulate the current flowing in the lamp rather than the applied voltage. As an example, a 450 W lamp operates normally at 18 V and 25 A.
The use of the xenon technology has spread into the consumer market with the introduction in 1991 of xenon headlamps for cars. In this lamp the glass capsule is small and the arc spans only a few millimetres. Additions of mercury and salts of sodium and scandium improve the lumen output of the lamp significantly, the xenon gas being used only to provide instant light upon the ignition of the lamp.
These are structurally similar to short-arc lamps except that the arc-containing portion of the glass tube is greatly elongated. When mounted within an elliptical reflector, these lamps are frequently used to simulate sunlight. Typical uses include solar cell testing, solar simulation for age testing of materials, rapid thermal processing, and material inspection.
XBO lamps are short arc lamps in which the discharge arc fires in a pure xenon atmosphere under high pressure. XBO lamps have a very good color rendering and extremely high luminance. For this reason they are often used in light guide systems, e.g. for endoscopy or dental technology usage.
A mercury-vapor lamp is a gas discharge lamp that uses mercury in an excited state to produce light. The arc discharge is generally confined to a small fused quartz arc tube mounted within a larger borosilicate glass bulb. The outer bulb may be clear or coated with a phosphor; in either case, the outer bulb provides thermal insulation, protection from ultraviolet radiation, and a convenient mounting for the fused quartz arc tube.
Mercury vapor lamps (and their relatives) are often used because they are relatively efficient. Phosphor coated bulbs offer better color rendition than either high- or low-pressure sodium vapor lamps. Mercury vapor lamps also offer a very long lifetime, as well as intense lighting for several special purpose applications.
Charles Wheatstone observed the spectrum of an electric discharge in mercury vapor in 1835, and noted the ultraviolet lines in that spectrum. In 1860, John Thomas Way used arc lamps operated in a mixture of air and mercury vapor at atmospheric pressure for lighting. The German physicist Leo Arons (1860-1919) studied mercury discharges in 1892 and developed a lamp based on a mercury arc.  A commercially-important mercury vapor lamp was patented in 1901 by Peter Cooper Hewitt  but it produced light with very little red component, so it was not a general purpose light source. It was used for industrial lighting and (monochrome) photography. The ultraviolet light from mercury vapor lamps was applied to water treatment by 1910. The Hewitt lamps used a large amount of mercury. In the 1930's, improved lamps of the modern form, developed by the Osram-GEC company, General Electric company and others lead to widespread use of mercury vapor lamps for general lighting.
The mercury vapor lamp is a negative resistance device and requires a ballast to prevent it from taking excessive current. The auxiliary components are substantially similar to the ballasts used with fluorescent lamps. In fact, the first British fluorescent lamps were designed to operate from 80-watt mercury vapor ballasts.
Also like fluorescent lamps, mercury vapor lamps usually require a starter, which is usually contained within the mercury vapor lamp itself. A third electrode is mounted near one of the main electrodes and connected through a resistor to the other main electrode. When power is applied, there is sufficient voltage to strike an arc between the starting electrode and the adjacent main electrode. This arc discharge eventually provides enough ionized mercury to strike an arc between the main electrodes. Occasionally, a thermal switch will also be installed to short the starting electrode to the adjacent main electrode, completely suppressing the starting arc once the main arc strikes.
A closely-related lamp design called the metal halide lamp uses various compounds in an amalgam with the mercury. Sodium iodide and Scandium iodide are commonly in use. These lamps can produce much better quality light without resorting to phosphors. If they use a starting electrode, there is always a thermal shorting switch to eliminate any electrical potential between the main electrode and the starting electrode once the lamp is lit. (This electrical potential in the presence of the halides can cause the failure of the glass/metal seal). More modern metal halide systems do not use a separate starting electrode; instead, the lamp is started using high voltage pulses as with high-pressure sodium vapor lamps. "MetalArc" is Osram Sylvania's trademark for their metal halide lamps; "Arcstream" and "MultiVapor" are General Electric's trademark. Besides their use in traditional outdoor lighting, these lamps now appear in most computer and video projectors. However, Philips' UHP lamp, introduced in 1995, contains only mercury. As an example of application and efficiency of mercury lamps, the 61" Samsung DLP rear projection TV (HL-S6187W) uses a 132-watt Philips UHP lamp.
There are mercury vapor lamps with a filament inside connected in series with the arc tube that functions as an electrical ballast. This is the only kind of mercury vapor lamp that should be connected directly to the mains without an external ballast. These lamps have only the same or slightly higher efficiency than incandescent lamps of similar size, but have a longer life. They give light immediately on startup, but usually needs a few minutes to restrike if power has been interrupted. Because of the light emitted by the filament, they have slightly better color rendering properties than mercury vapor lamps. The color temperature is higher than incandescent lamps.
When a mercury vapor lamp is first turned on, it will produce a dark blue glow because only a small amount of the mercury is ionized and the gas pressure in the arc tube is very low, so much of the light is produced in the ultraviolet mercury bands. As the main arc strikes and the gas heats up and increases in pressure, the light shifts into the visible range and the high gas pressure causes the mercury emission bands to broaden somewhat, producing a light that appears more nearly white to the human eye, although it is still not a continuous spectrum. Even at full intensity, the light from a mercury vapor lamp with no phosphors is distinctly bluish in color. The pressure in the silica glass tube rises to approximately one atmosphere once the bulb has reached its working temperature. If the discharge should be interrupted (e.g. by interruption of the electric supply), it is not possible for the lamp to restrike until the bulb cools enough for the pressure to fall considerably.
To correct the bluish tinge, many mercury vapor lamps are coated on the inside of the outer bulb with a phosphor that converts some portion of the ultraviolet emissions into red light. This helps to fill in the otherwise very-deficient red end of the electromagnetic spectrum. These lamps are generally called "color corrected" lamps. Most modern mercury vapor lamps have this coating. One of the original complaints against mercury lights was they tended to make people look like "bloodless corpses" because of the lack of light from the red end of the spectrum. A common method of correcting this problem before phosphors were used was to operate the mercury lamp in conjunction with an incandescent lamp. There is also an increase in red color (e.g., due to the continuous radiation) in ultra-high pressure mercury vapor lamps (usually greater than 200 atm.), which has found application in modern compact projection devices. When outside, coated or color corrected lamps can usually be identified by a blue "halo" around the light being given off.
The strongest peaks of the emission line spectrum are
|Wavelength (nm)||Name (see photoresist)|
In low-pressure mercury-vapor lamps only the lines at 184 nm and 253 nm are present. Only the light at 253 nm is usable unless synthetic quartz is used to manufacture the tube as the line is otherwise absorbed. In medium-pressure mercury-vapor lamps, the lines from 200-600 nm are present. The lamps can be constructed to emit primarily in the UV-A (around 400 nm)or UV-C (around 250 nm). High-pressure mercury-vapor lamps are those lamp commonly used for general lighting purposes. They emit primarily in the blue and green.
Low-pressure mercury-vapor lamps usually have a quartz bulb in order to allow the transmission of short wavelength light. If synthetic quartz is used, then the transparency of the quartz is increased further and an emission line at 185 nm is observed also. Such a lamp can then be used for the cleaning or modification of surfaces. The line 185 nm will create ozone in an oxygen containing atmosphere, which helps in the cleaning process, but is also a health hazard.
For placements where light pollution is of prime importance (for example, an observatory parking lot), low pressure sodium is preferred. As it emits light on only one wavelength, it is the easiest to filter out. Mercury vapor lamps without any phosphor are second best; they produce only a few distinct mercury lines that need to be filtered out.
The use of mercury vapor lamps for lighting purposes will be banned in the EU in 2015. As this ban is designed to phase out less efficient lamps it does not affect the use of mercury in compact fluorescent lamp nor the use of mercury lamps for purposes other than lighting. In the USA, ballasts and fixtures were banned in 2008. Because of this, several manufacturers have begun selling replacement compact fluorescent lamps for mercury vapor fixtures, which do not require modifications to the existing fixture.
All mercury vapor lamps (including metal halide lamps) must contain a feature (or be installed in a fixture that contains a feature) that prevents ultraviolet radiation from escaping. Usually, the borosilicate glass outer bulb of the lamp performs this function but special care must be taken if the lamp is installed in a situation where this outer envelope can become damaged. There have been documented cases of lamps being damaged in gymnasiums by a ball hitting it. Sun burns and eye inflammation have resulted. When used in locations like gyms, the fixture should contain a strong outer guard or an outer lens to protect the lamp's outer bulb. Also, special "safety" lamps are made that will deliberately burn out if the outer glass is broken. This is usually achieved by using a thin carbon strip, which will burn up in the presence of air, to connect one of the electrodes.
Even with these methods, some UV radiation can still pass through the outer bulb of the lamp. This causes the aging process of some plastics used in the construction of luminaires to be accelerated, leaving them significantly discolored after only a few years' service. Polycarbonate suffers particularly from this problem, and it is not uncommon to see fairly new polycarbonate surfaces positioned near the lamp to have turned a dull, 'ear-wax'-like color after only a short time. Certain polishes, such as Brasso, can be used to remove some of the yellowing, but usually only with limited success.
Mercury vapor lamps rarely burn out completely but suffer from lumen depreciation. The lamp produces 50% less light every five years, to the point of becoming ineffective while still drawing the same amount of power it drew when it was new. This comes about because the emitter is deposited as a film darkening the arctube wall and reducing light output.
Ultra high pressure mercury vapor lamps are used in the area of photolithography to expose various photoresists. The unique spectral emission characteristics of mercury vapor lamps are ideal for photoresists, the most common of which are generally photosensitive between 350 and 500 nm wavelengths.
Hydrargyrum medium-arc iodide, or HMI, is a Osram brand metal-halide gas discharge medium arc-length lamp manufactured for the film and entertainment industry. Hydrargyrum is Latin for mercury (Hg). The term HMI has become a genericized trademark for all similar high-quality metal-halide lamps made for film and entertainment, regardless of manufacturer.
An HMI lamp uses mercury vapour mixed with metal halides in a quartz-glass envelope, with two tungsten electrodes of medium arc separation. Unlike traditional lighting units using incandescent light bulbs, HMIs need electrical ballasts, which are separated from the head via a header cable, to limit current and supply the proper voltage. The lamp operates by creating an electrical arc between two electrodes within the bulb that excites the pressurized mercury vapour and metal halides, and provides very high light output with greater efficacy than incandescent lighting units. The efficiency advantage is near fourfold, with approximately 85–108 lumens per watt of electricity. Unlike tungsten-halogen lamps where the halide gas is used to regenerate the filament and keep the evaporated tungsten from darkening, the mercury vapour and the metal halides in HMI lamps are what emit the light. The high CRI and color temperature are due to the specific lamp chemistries.
In the late 1960s German television producers sought out lamp developer OSRAM to create a less expensive replacement for incandescent lights for the film industry. Osram developed and began producing HMI bulbs at their request.
Philips produced a variation on the HMI, a single-ended version called MSR (medium source rare-earth). It uses a standard two-prong lampbase. In order to avoid the colour shift during use they added a secondary envelope around the gas-chamber. Several other bulb variations exist, including GEMI (General Electric metal iodide), CID (compact indium discharge; Thorne, UK), CSI (compact source iodine; Thorne, UK), DAYMAX (made by ILC), and BRITE ARC (Sylvania). All are variations and different names for essentially the same concept.
Within the last ten years, a lot of research has gone into making HMI bulbs smaller because of their use in moving light fixtures such as those manufactured by Vari-Lite, Martin, and Highend. Philips' main contribution after this was the invention of a phosphor coating on the weld of the filament to the molybdenum foil that reduces oxidization and early failures at that point, making that area capable of withstanding extreme heat.
Multi-kilowatt HMI lights are used in the film industry and for large-screen slide projection because of their daylight-balanced light output, as well as their efficiency.
Similar to fluorescent lights, HMIs present problems with color temperature when used for film or video lighting applications. Unlike incandescent-lighting units, which are blackbody radiators limited to a theoretical maximum of 3680 K (the melting point of tungsten), HMI lamps, like all gas discharge lighting, emit the emission spectral lines of its constituent elements, specifically chosen so that combined, they resemble the blackbody spectrum of a 6000 K source. This closely matches the color of sunlight (but not skylight), because the sun's surface is a 6000 K blackbody radiator.
With HMI bulbs, color temperature varies significantly with lamp age. A new bulb generally will output at a color temperature close to 15,000 K during its first few hours. As the bulb ages, the color temperature reaches its nominal value of around 5600 K or 6000 K. With age, the arc length becomes larger as more of the electrodes burn away. This requires greater voltage to sustain the arc, and as voltage increases, color temperature decreases proportionately at a rate of approximately 0.5–1 kelvin for every hour burnt. For this reason, and other safety reasons, HMI bulbs are not recommended to be used past half their lifetime.
HMI bulbs (like all arc bulbs) need a current limiting unit to function. Two possibilities to do that are described in the ballast section below. The problem of flickering exists only when using the bulb in combination with magnetic ballast (electronic ballasts produce flickerfree light). HMI bulbs (running with magnetic ballast) present an inherent problem of possibly producing light on film or video with a noticeable flicker. This is caused by the method by which the unit produces light. An HMI, like an incandescent lighting unit, runs on mains power, which means that the lamp cycles on and off 100 or 120 times per second (twice for every line voltage cycle). Although not visible to the human eye, a film or video camera must be properly synchronized to this cycle or each frame recorded will show different light output. Although incandescent lamps also run off mains power, they don't exhibit perceptible flicker because their filaments don't cool down enough between cycles for their light output to decrease very much. For HMI lamps, flicker can be avoided by the use of electronic ballasts that cycle at frequencies thousands of times faster than the mains frequency.
To power an HMI bulb, special ballasts act as an ignitor to start the arc, and then regulate it by acting as a choke. Two types of ballasts exist: magnetic and electronic (square-wave or flicker-free). Magnetic ballasts are generally much heavier and bulkier than electronic ballasts, as they consist primarily of a network of large inductors. They are usually cheaper than electronic ballasts. Since the magnetic type of ballast does not maintain the discharge continuously, the lamp actually extinguishes at zero-crossings of the mains waveform; unless the camera is locked to the mains waveform, the difference in frequency between the lamp and the shutter will produce a beat frequency that is visible in the resulting recording. This is why TV standards typically use the power grid frequency as their basic frame rate. Magnetic ballasts are simple devices compared to electronic ballasts. Essentially, a magnetic ballast is a large, heavy transformer coil that uses a simple principle to generate the high startup voltages needed to create an arc in a cold lamp. Input power is routed to a choke coil connected between the main input and the lamp. The coil may be tapped in several places to provide for various input voltages (120 V or 240 V) and a high start-up voltage. Capacitors are also included to compensate for the inductance of the coil and improve the power factor. Because of the high amount of current through the ballast, a low humming sound is often heard due to magnetostriction of the ballast iron laminations. Some magnetic ballasts have insulation around the coil for silent operation.
Within the last ten years, electronic flicker-free (or Square-Wave) ballasts have become increasingly popular and affordable as an alternative to magnetic ballasts by eliminating most of the problems associated with HMI flicker. Unfortunately, their operation is not as simple as a magnetic ballast. Electronic ballasts can be thought of as operating in three stages—a DC intermediate converter, a power module, and an AC inverter. Power initially flows through the main breakers into an RF mains filter that prevents the flow of noise back onto the incoming power line. Then, rectifiers and capacitors charge and discharge to invert the negative half of the AC cycle and convert the line to positive DC voltage. This is called the DC intermediate. In the second stage, a buck converter draws from the DC intermediate and regulates current to the final power electronics via an electronic control board. This control board carefully adjusts the high frequency duty cycle of its transistors to maintain optimum color and light output as the lamp ages. Finally, the regulated current is inverted by an LF-converter board that uses four Insulated Gate Bipolar Transistors (IGBTs) to switch the DC at precisely 60 Hz into a square wave AC (unlike the sinusoidal pattern of line AC). Leaders in this field include Power Gems Corp, B&S, & Mytronic.
By using a square-wave output that is not referenced to the line cycle rate, a flicker-free output can be produced. Since the IGBTs switch on and off at a regulated cycle rate, a generator can be slightly off-speed and the lamp will still be flicker-free, which is not the case with a standard magnetic ballast. The square wave nature of the output results in a straight-line power output from the lamp. The time where cathodes aren't emitting electrons of high enough energy is very short, meaning that safe (flicker-free) filming can occur at camera framerates up to 10,000 frame/s on most electronic ballasts.
Unfortunately, this very sharp switching on and off inherent to the square-waveform causes extremely high frequency vibrations in the lamp. A square wave can be thought of as an infinite sum of odd-numbered harmonics, which will include frequencies at the resonant frequency of the bulb, causing it to vibrate at that frequency like a bell or whistle. The lamp housing does not help this, acting as a resonating chamber that amplifies the noise and presents a problem for sync-sound recording for film and video. To correct this, most electronic ballasts are equipped with a silent mode that eliminates the higher frequencies, but rounds off the voltage transition, causing the same flicker issue with magnetics, though to a lesser extent. This mode provides safe, flicker-free filming at framerates up to 24 frame/s on most electronic ballasts.
In addition to solving the problems of flicker, electronic ballasts also provide other advantages over magnetic ballasts. With a square wave voltage the cathodes spend much more time emitting electrons and exciting the plasma, there is a gain of 5–10% in light output. The square-wave nature of the power flow allows lamp life to be extended by as much as 20%. Most modern ballasts are now also equipped with a dimmer, which uses pulse-width modulation to dim the lamp up to 50%, or as much as one stop of light. Unlike a tungsten-based light, which has a negative color temperature shift with a drop in power, the mercury emission spectra takes over with a drop in power (approximately 200 K bluer at 50% output).
HMI lamps are approximately the same color temperature as the sun, and as with most other mercury-based high intensity discharge lamps, generate ultra-violet light. Each HMI light has a UV safety glass cover that should be used to protect persons who may be in front of the light. Exposure to an unprotected lamp can cause retinal damage and severe skin burns.
HMI lamps can reach ignition voltages of up to 70,000 V when striking hot, and are considered very dangerous if miswired. It is good practice to strike the light from the ballast and not the head, in the event that there is a short circuit in the lamp head. Proper striking procedures should be followed as well, such as calling out a vocal warning whenever a light is turned on to warn persons in the area. Also, the header cable should be properly and securely connected (most header cables will twist and click into place).
In addition to these concerns, HMI lamps have been known to explode violently at the end of their lifetime or if stressed enough. While not as violent as the explosion of a xenon short-arc bulb, they still require caution. As a result, HMI lamps should not be used past half their rated lifetime, and care should be taken with larger lamps when striking (turning on the lamp), as a lamp is most likely to explode within the first five minutes of striking. Care should also be taken transporting the lamp and replacing lamps. The gasses in an HMI lamp are under pressure, which increases with temperature. Dropping the lamp could result in an explosion, sending hot quartz glass flying. As with quartz-halogen bulbs, care should be taken not to touch the glass directly as skin oils can attract heat and cause a weak point on the bulb. Most lamp housing designs are inherently tougher and thicker than traditional tungsten units so that in the event of a bulb explosion, those nearby are protected from flying debris. There is the possibility of the front lens element on the lamp head cracking from thermal shock. Proper safety procedures should be followed when using HMI units, as they can be quite dangerous if misused.
Hydrargyrum quartz iodide (HQI) is a special type of high-intensity discharge (or HID) lighting, where the light is produced by an electrical arc through a gas. Hydrargyrum is the Latin name for the element mercury. When heated, mercury vapour is created inside the lamp, and deposited when it cools.
An HQI lamp consists of a protective outer glass shield surrounding two heavy wires which are inserted into each end of a smaller inner bulb containing a gas. The lamp is powered by an electrical ballast, which regulates the current flow through the arc in the smaller inner lamp. Like all HID lamps, HQI lamps operate under high pressure and temperature, and require special light fixtures for safe use.
HQI lamps can produce different color temperatures when manufactured with different metal halides. They are relatively efficient light sources producing a high lumen per watt ratio (approximately 6x that of incandescent lamps).
Like HMI, HQI lamps are subsets (or types) of metal halide lamps, which in turn are subsets of high-intensity discharge (HID) lamps. They should not be confused with quartz halogen lamps, which are a specialized type of incandescent lamp.
Metal-halide lamps, a member of the high-intensity discharge (HID) family of lamps, produce high light output for their size, making them a compact, powerful, and efficient light source. By adding rare earth metal salts to the mercury vapor lamp, improved luminous efficacy and light color is obtained. Originally created in the late 1960s for industrial use, metal-halide lamps are now available in numerous sizes and configurations for commercial and residential applications.
Like most HID lamps, metal halide lamps operate under high pressure and temperature, and require special fixtures to operate safely.
Since the lamp is small compared to a fluorescent or incandescent lamp of the same light level, relatively small reflective luminaires can be used to direct the light for different applications (flood lighting outdoors, or lighting for warehouses or industrial buildings).
Metal-halide lamps are used both for general lighting purposes, and for very specific applications that require specific UV or blue-frequency light.
Because of their wide spectrum, they are used for indoor growing applications, in athletic facilities and are quite popular with reef aquarists, who need a high intensity light source for their corals.
Another widespread use for such lamps is in professional lighting fixtures, where they are commonly known as MSD lamps and are generally used in 150, 250, 400, 575 and 1,200 watt ratings, especially intelligent lighting.
Most LCD, DLP, high wattage light applications and film projectors use metal-halide lamps as their light source.
Like other gas-discharge lamps such as the very similar mercury-vapor lamps, metal-halide lamps produce light by making an electric arc in a mixture of gases. In a metal-halide lamp, the compact arc tube contains a high-pressure mixture of argon, mercury, and a variety of metal halides. The mixture of halides will affect the nature of light produced, influencing the correlated color temperature and intensity (making the light bluer, or redder, for example). The argon gas in the lamp is easily ionized, and facilitates striking the arc across the two electrodes when voltage is first applied to the lamp. The heat generated by the arc then vaporizes the mercury and metal halides, which produce light as the temperature and pressure increases.
Common operating conditions inside the arc tube are 5-50 atm or more (70–700 psi or 500-5000 kPa) and 1000-3000 °C. Like all other gas-discharge lamps, metal-halide lamps require auxiliary equipment to provide proper starting and operating voltages and regulate the current flow in the lamp. About 24% of the energy used by metal-halide lamps produces light (65–115 lm/W), making them substantially more efficient than incandescent bulbs.
Metal-halide lamps consist of an arc tube with electrodes, an outer bulb, and a base.
Inside the fused quartz arc tube two tungsten electrodes doped with thorium, are sealed into each end and current is passed to them by molybdenum foil seals in the fused silica. It is within the arc tube that the light is actually created.
Besides the mercury vapor, the lamp contains iodides or sometimes bromides of different metals. Scandium and sodium are used in some types, thallium, indium and sodium in European Tri-Salt models, and more recent types use dysprosium for high colour temperature, tin for lower colour temperature. Holmium and thulium are used in some very high power movie lighting models. Gallium or lead is used in special high UV-A models for printing purposes. The mixture of the metals used defines the color of the lamp. Some types for festive or theatrical effect use almost pure iodides of thallium, for green lamps, and indium, for blue lamps. An alkali metal, (sodium or potassium), is almost always added to reduce the arc impedance, allowing the arc tube to be made sufficiently long and simple electrical ballasts to be used. A noble gas, usually argon, is cold filled into the arc tube at a pressure of about 2 kPa to facilitate starting of the discharge.
The ends of the arc tube are often externally coated with white infrared reflective zirconium silicate or zirconium oxide to reflect heat back onto the electrodes to keep them hot and thermionically emitting. Some bulbs have a phosphor coating on the inner side of the outer bulb to improve the spectrum and diffuse the light.
In the mid-1980s a new type of metal-halide lamp was developed, which, instead of a quartz (fused silica) arc tube as used in mercury vapor lamps and previous metal-halide lamp designs, use a sintered alumina arc tube similar to what has been used in the high pressure sodium lamp. This development reduces the effects of ion creep that plagues fused silica arc tubes. During their life, because of high UV radiation and gas ionization, sodium and other elements tends to migrate into the quartz tube, resulting in depletion of light emitting material and so, cycling. The sintered alumina arc tube does not allow the ions to creep through, maintaining a more constant colour over the life of the lamp. These are usually referred as ceramic metal-halide lamps or CMH lamps.
Most types are fitted with an outer glass bulb to protect the inner components and prevent heat loss. The outer bulb can also be used to block some or all of the UV light generated by the mercury vapor discharge, and can be composed of specially doped "UV stop" fused silica. Ultraviolet protection is commonly employed in single ended (single base) models and double ended models that provide illumination for nearby human use. Some high powered models, particularly the Lead-Gallium UV printing models and models used for some types of sports stadium lighting do not have an outer bulb. The use of a bare arc tube can allow transmission of UV or precise positioning within the optical system of a luminaire. The cover glass of the luminaire can be used to block the UV, and can also protect people or equipment if the lamp should fail by exploding.
Some types have an Edison screw metal base, for various power ratings between 10 and 18,000 watts. Other types are double-ended, as depicted above, with R7s-24 bases composed of ceramic, along with metal connections between the interior of the arc tube and the exterior. These are made of various alloys (such as iron-cobalt-nickel) that have a thermal coefficient of expansion that matches that of the arc tube.
Metal-halide lamps require electrical ballasts to regulate the arc current and deliver the proper voltage to the arc. Like high-pressure mercury vapour lamps, some metal-halide bulbs contain a third electrode to initiate the arc when the lamp is first lit (which generates a slight flicker when the lamp is first turned on). Pulse-start metal-halide lamps don't contain a starting electrode, but they require an ignitor to generate a high-voltage (1–5 kV on cold strike, over 30 kV on hot restrike) pulse to start the arc. American National Standards Institute (ANSI) lamp-ballast system standards establish parameters for all metal-halide components (with the exception of some newer products).
Electronic ballasts include ignitor and ballast into a single package. These ballasts use high-frequency to drive the lamps. Because they have less loss than a line-frequency "iron" ballast, they are more energy efficient. High-frequency operation does not increase lamp efficacy as for fluorescent lamps.
Because of the whiter and more natural light generated, metal-halide lamps were initially preferred to the bluish mercury vapor lamps. With the introduction of specialized metal-halide mixtures, metal-halide lamps are now available with a correlated color temperature from 3,000 K to over 20,000 K. Color temperature can vary slightly from lamp to lamp, and this effect is noticeable places where many lamps are used. Because the lamp's color characteristics tend to change during lamp's life, color is measured after the bulb has been burned for 100 hours (seasoned) according to ANSI standards. Newer metal-halide technology, referred to as "pulse start," has improved color rendering and a more controlled kelvin variance (±100 to 200 kelvins).
The color temperature of a metal-halide lamp can also be affected by the electrical characteristics of the electrical system powering the bulb and manufacturing variances in the bulb itself. If a metal-halide bulb is underpowered, because of the lower operating temperature, its light output will be bluish because of the evaporation of mercury alone. This phenomenon can be seen during warmup, when the arc tube has not yet reached full operating temperature and the halides have not fully vaporized. The inverse is true for an overpowered bulb, but this condition can be hazardous, leading possibly to arc-tube explosion because of overheating and overpressure.
A "cold" (below operating temperature) metal-halide lamp cannot immediately begin producing its full light capacity because the temperature and pressure in the inner arc chamber require time to reach full operating levels. Starting the initial argon arc sometimes takes a few seconds, and the warm up period can be as long as five minutes (depending upon lamp type). During this time the lamp exhibits different colors as the various metal halides vaporize in the arc chamber.
If power is interrupted, even briefly, the lamp's arc will extinguish, and the high pressure that exists in the hot arc tube will prevent restriking the arc; with a normal ignitor a cool-down period of 5–10 minutes will be required before the lamp can be re-started, but with special ignitors with specially designed lamps, the arc can be immediately re-established. On fixtures without instant restrike capability, a momentary loss of power can can mean no light for several minutes. For safety reasons, many metal-halide fixtures have a backup tungsten-halogen incandescent lamp that operates during cool-down and restrike. Once the metal halide restrikes and warms up, the incandescent safety light is switched off. A warm lamp also tends to take more time to reach its full brightness than a lamp that is started completely cold.
Most hanging ceiling lamps tend to be passively cooled, with a combined ballast and lamp fixture; immediately restoring power to a hot lamp before it has re-struck can make it take even longer to relight, because of power consumption and heating of the passively cooled lamp ballast that is attempting to relight the lamp.
At the end of life, metal-halide lamps exhibit a phenomenon known as cycling. These lamps can be started at a relatively low voltage but as they heat up during operation, the internal gas pressure within the arc tube rises and more and more voltage is required to maintain the arc discharge. As a lamp gets older, the maintaining voltage for the arc eventually rises to exceed the voltage provided by the electrical ballast. As the lamp heats to this point, the arc fails and the lamp goes out. Eventually, with the arc extinguished, the lamp cools down again, the gas pressure in the arc tube is reduced, and the ballast can once again cause the arc to strike. This causes the lamp to glow for a while and then goes out, repeatedly. In rare occurrences the lamp explodes at the end of its useful life.
Modern electronic ballast designs detect cycling and give up attempting to start the lamp after a few cycles. If power is removed and reapplied, the ballast will make a new series of startup attempts.
All HID arc tubes deteriorate in strength over their lifetime because of various factors, such as chemical attack, thermal stress and mechanical vibration. As the lamp ages the arc tube becomes discoloured, absorbing light and getting hotter. The tube will continue to become weaker until it eventually fails, causing the break up of the tube.
Although such failure is associated with end of life, an arc tube can fail at any time even when new, because of unseen manufacturing faults such as microscopic cracks. However, this is quite rare. Manufacturers typically "season" new lamps to check for manufacturing defects before the lamps leave the manufacturer's premises.
Since a metal-halide lamp contains gases at a significant high pressure, failure of the arc tube is inevitably a violent event. Fragments of arc tube are launched, at high velocity, in all directions, striking the outer bulb of the lamp with enough force to cause it to break. If the fixture has no secondary containment (e.g. a lens, bowl or shield) then the extremely hot pieces of debris will fall down onto people and property below the light, likely resulting in serious injury, damage, and possibly causing a major building fire if flammable material is present.
The risk of a "nonpassive failure" of an arc tube is very small. According to information gathered by the National Electrical Manufacturers Association (www.nema.org), there are approximately 40 million metal-halide systems in North America alone, and only a very few instances of nonpassive failures have occurred. Although it is not possible to predict, or eliminate the risk, of a metal-halide lamp exploding, there are several precautions that can be taken to reduce the risk:
Also, there are measures that can be taken to reduce the damage caused should a lamp fail violently:
Although an excellent source of lighting for the reef aquarium, there has been concern voiced by some aquarists over the potential ill-effects of close-range contact with metal-halide lighting that is demanded by the hobby. Some individuals have noticed temporary blurred vision even after very brief exposure to metal-halide lighting. This blurring of vision could be linked to photokeratitis (snow blindness) – the result of unprotected exposure to ultraviolet (UV) radiation.
Broken and unshielded high-intensity metal-halide bulbs have been known to cause eye and skin injuries, particularly in school gymnasiums. See the following article from the FDA: Ultraviolet Radiation Burns from High Intensity Metal Halide and Mercury Vapor Lighting Remain a Public Health Concern. Also see: Teachers battle dangerous lighting conditions and Photokeratitis and UV-Radiation Burns Associated With Damaged Metal Halide Lamps.
A sodium vapor lamp is a gas discharge lamp that uses sodium in an excited state to produce light. There are two varieties of such lamps: low pressure and high pressure. Because sodium vapor lamps cause less light pollution than mercury-vapor lamps, many cities that have large astronomical observatories employ them.
Low-pressure sodium (LPS) lamps have a borosilicate glass gas discharge tube (arc tube) containing solid sodium and a small amount of neon and argon gas Penning mixture to start the gas discharge. The discharge tube may be linear (SLI lamp)  or U-shaped. When the lamp is turned on it emits a dim red/pink light to warm the sodium metal and within a few minutes it turns into the common bright yellow as the sodium metal vaporizes. These lamps produce a virtually monochromatic light averaging a 589.3 nm wavelength (actually two dominant spectral lines very close together at 589.0 and 589.6 nm). As a result, the colors of illuminated objects are not easily distinguished because they are seen almost entirely by their reflection of this narrow bandwidth yellow light.
LPS lamps have an outer glass vacuum envelope around the inner discharge tube for thermal insulation, which improves their efficiency. Earlier types of LPS lamps had a detachable dewar jacket (SO lamps). Lamps with a permanent vacuum envelope (SOI lamps) were developed to improve thermal insulation. Further improvement was attained by coating the glass envelope with an infrared reflecting layer of indium tin oxide, resulting in SOX lamps.
LPS lamps are the most efficient electrically-powered light source when measured for photopic lighting conditions—up to 200 lm/W, primarily because the output is light at a wavelength near the peak sensitivity of the human eye. As a result they are widely used for outdoor lighting such as street lights and security lighting where faithful color rendition is considered unimportant. LPS lamps are available with power ratings from 10 W up to 180 W; however, longer bulb lengths create design and engineering problems.
LPS lamps are more closely related to fluorescent than high intensity discharge lamps because they have a low–pressure, low–intensity discharge source and a linear lamp shape. Also like fluorescents they do not exhibit a bright arc as do other HID lamps; rather they emit a softer luminous glow, resulting in less glare. Unlike HID lamps, which can go out during a voltage dip, low pressure sodium lamps restrike to full brightness rapidly.
Another unique property of LPS lamps is that, unlike other lamp types, they do not decline in lumen output with age. As an example, mercury vapor HID lamps become very dull towards the end of their lives, to the point of being ineffective, while continuing to consume full rated electrical use. LPS lamps, however, do increase energy usage slightly (about 10%) towards their end of life, which is generally around 18,000 hours for modern lamps.
High-pressure sodium (HPS) lamps are smaller and contain additional elements such as mercury, and produce a dark pink glow when first struck, and a pinkish orange light when warmed. Some bulbs also briefly produce a pure to bluish white light in between. This is probably from the mercury glowing before the sodium is completely warmed. The sodium D-line is the main source of light from the HPS lamp, and it is extremely pressure broadened by the high sodium pressures in the lamp; because of this broadening and the emissions from mercury, colors of objects under these lamps can be distinguished. This leads them to be used in areas where good color rendering is important, or desired. Thus, its new model name SON is the variant for "sun" (a name used primarily in Europe and the UK). HPS Lamps are favoured by indoor gardeners for general growing because of the wide colour-temperature spectrum produced and the relatively efficient cost of running the lights.
High pressure sodium lamps are quite efficient—about 100 lm/W—when measured for photopic lighting conditions. The higher powered versions of 600 W have an efficacy of even 150lm/W. They have been widely used for outdoor lighting such as streetlights and security lighting. Understanding the change in human color vision sensitivity from photopic to mesopic and scotopic is essential for proper planning when designing lighting for roads.
Because of the extremely high chemical activity of the high pressure sodium arc, the arc tube is typically made of translucent aluminium oxide. This construction led General Electric to use the tradename "Lucalox" for their line of high-pressure sodium lamps.
Xenon at a low pressure is used as a "starter gas" in the HPS lamp. It has the lowest thermal conductivity and lowest ionization potential of all the non-radioactive noble gases. As a noble gas, it does not interfere with the chemical reactions occurring in the operating lamp. The low thermal conductivity minimizes thermal losses in the lamp while in the operating state, and the low ionization potential causes the breakdown voltage of the gas to be relatively low in the cold state, which allows the lamp to be easily started.
A variation of the high pressure sodium, the White SON, introduced in 1986, has a higher pressure than the typical HPS/SON lamp, producing a color temperature of around 2700 K, with a CRI of 85, greatly resembling the color of an incandescent light. These are often used indoors in cafes and restaurants to create a particular atmosphere. However, these lamps suffer from higher purchase cost, shorter life, and lower light efficiency.
An amalgam of metallic sodium and mercury lies at the coolest part of the lamp and provides the sodium and mercury vapor that is needed to draw an arc. The temperature of the amalgam is determined to a great extent by lamp power. The higher the lamp power, the higher will be the amalgam temperature. The higher the temperature of the amalgam, the higher will be the mercury and sodium vapor pressures in the lamp. An increase in these metal pressures will cause an increase in the electrical resistance of the lamp. As the temperature rises, the flow of current being maintained constant results in an increase in power until the nominal power is reached. For a given voltage, there are generally three modes of operation:
The first and last states are stable, because the lamp resistance is weakly related to the voltage, but the second state is unstable. Any anomalous increase in current will cause an increase in power, causing an increase in amalgam temperature, which will cause a decrease in resistance, which will cause a further increase in current. This will create a runaway effect, and the lamp will jump to the high-current state (#3). Because actual lamps are not designed to handle this much power, this would result in catastrophic failure. Similarly, an anomalous drop in current will drive the lamp to extinction. It is the second state that is the desired operating state of the lamp, because a slow loss of the amalgam over time from a reservoir will have less effect on the characteristics of the lamp than a fully evaporated amalgam. The result is an average lamp life in excess of 20,000 hours.
In practical use, the lamp is powered by an AC voltage source in series with an inductive "ballast" in order to supply a nearly constant current to the lamp, rather than a constant voltage, thus assuring stable operation. The ballast is usually inductive rather than simply being resistive to minimize resistive losses. Because the lamp effectively extinguishes at each zero-current point in the AC cycle, the inductive ballast assists in the reignition by providing a voltage spike at the zero-current point.
The light from the lamp consists of atomic emission lines of mercury and sodium, but is dominated by the sodium D-line emission. This line is extremely pressure (resonance) broadened and is also self-reversed because of absorption in the cooler outer layers of the arc, giving the lamp its improved color rendering characteristics. In addition, the red wing of the D-line emission is further pressure broadened by the Van der Waals forces from the mercury atoms in the arc.
For placements where light pollution is of prime importance, such as an astronomical observatory parking lot, or a large city nearby an astronomical observatory, low pressure sodium is preferred. Such lamps emit light on just one dominant spectral line (with other far-weaker lines), and therefore is the easiest to filter out. One consequence of widespread public lighting is that on cloudy nights, cities with enough lighting are illuminated by light reflected off the clouds. As sodium vapor lights are often the source of urban illumination, this turns the sky a tinge of orange. If the sky is clear or hazy, the light will radiate over large distances, causing large enough cities to be recognizable by an orange glow when viewed from outside the city.
At the end of life, high-pressure sodium lamps exhibit a phenomenon known as cycling, which is caused by a loss of sodium in the arc. Sodium is a highly reactive element, and is easily lost by reacting with the arc tube made of aluminum oxide and the products are sodium oxide and aluminum:
As a result, these lamps can be started at a relatively low voltage but as they heat up during operation, the internal gas pressure within the arc tube rises and more and more voltage is required to maintain the arc discharge. As a lamp gets older, the maintaining voltage for the arc eventually rises to exceed the maximum voltage output by the electrical ballast. As the lamp heats to this point, the arc fails and the lamp goes out. Eventually, with the arc extinguished, the lamp cools down again, the gas pressure in the arc tube is reduced, and the ballast can once again cause the arc to strike. The effect of this is that the lamp glows for a while and then goes out, repeatedly.
More sophisticated ballast designs detect cycling and give up attempting to start the lamp after a few cycles, as the repeated high voltage ignitions needed to restart the arc reduces the lifetime of the ballast. If power is removed and reapplied, the ballast will make a new series of startup attempts.
LPS lamp failure does not result in cycling; rather, the lamp will simply not strike or will maintain its dull red glow exhibited during the start up phase.
A deuterium arc lamp (or simply deuterium lamp) is a low-pressure gas-discharge light source often used in spectroscopy when a continuous spectrum in the ultraviolet region is needed.
A deuterium lamp uses a tungsten filament and anode placed on opposite sides of a nickel box structure designed to produce the best output spectrum. Unlike an incandescent bulb, the filament is not the source of light in deuterium lamps. Instead an arc is created from the filament to the anode, a similar process to arc lamps. Because the filament must be very hot before it can operate, it is heated for approximately twenty seconds before use. Because the discharge process produces its own heat, the heater is turned down after discharge begins. Although firing voltages are 300 to 500 volts, once the arc is created voltages drop to around 100 to 200 volts.
The arc created excites the molecular deuterium contained within the bulb to a higher energy state. The deuterium then emits light as it transitions back to its initial state. This continuous cycle is the origin of the continuous ultraviolet radiation. This process is not the same as the process of decay of atomic excited states (atomic emission), where electrons are excited and then emit radiation. Instead from the molecular emission process, where radiative decay of excited states, in this case of molecular deuterium (D2), causes the effect.
Because the lamp operates at high temperatures, normal glass housings cannot be used for a casing (which would also block UV radiation). Instead, a fused quartz, UV glass, or magnesium fluoride envelope is used depending on the specific function of the lamp.
The typical lifetime of a deuterium lamp is approximately 2000 hours (Most manufacturers guarantee 2000 hours, but newer lamps are consistently performing well out to 5000 hours and more).
The deuterium lamp emits radiation extending from 112 nm to 900 nm, although its continuous spectrum is only from 180 nm to 370 nm. The spectrum intensity does not actually decrease from 250nm to 300nm as shown in the spectrum plot above. The decrease in the plot is due to decreased efficiency at low wavelengths of the photo detector used to measure the lamp intensity. Deuterium Lamp's continuous spectrum is useful as both a reference in UV radiometric work and to generate a signal in various photometric devices.
Due to the high intensity of UV radiation emitted by the bulb, eye protection is suggested when using a deuterium bulb. Care must also be taken to avoid touching the bulb directly to avoid burns due to high operating temperatures. Touching the bulb directly even when cool can smudge the casing and therefore reduce output intensity.
Photron Deuterium Lamps
Deuterium Lamp Instrument Suitability
[hide]Lamps and lighting
Tanning lamps (sometimes called tanning bulbs in the United States or tanning tubes in Europe) are the part of a tanning bed, booth or other tanning device which produces ultraviolet light responsible for tanning. While there are literally hundreds of different kinds of tanning lamps, they can usually be classified in two basic groups: low pressure and high pressure. Within the industry, it is common to call high pressure units "bulbs" and low pressure units "lamps", although there are many exceptions and not everyone follows this example. This is likely due to the size of the unit, rather than the type. Both types require an oxygen free environment inside the lamp.
Fluorescent tanning lamps require an electrical ballast to provide power. While the resistance of an incandescent lamp filament inherently limits the current inside the lamp, tanning lamps do not and instead have negative resistance. They are plasma devices, like a neon sign, and will pass as much current as the external circuit will provide, even to the point of DIRSA self destruction. Thus a ballast is needed to regulate the current through them.
Tanning lamps are installed in a tanning bed, tanning booth, tanning canopy or free standing single bulb tanning unit. The quality of the tan (or how similar it is to a tan from the natural sun) depends upon the spectrum of the light that is generated from the lamps. Most tanning lamps produce much more UV than the sun on a typical day. This gives the user a faster base tan, but one that fades faster and offers less protection from the sun than a natural tan.
High pressure bulbs are 3 to 5 inches long and typically powered by a ballast with 250 to 2000 watts. The most common is the 400 watt variety that is used as an added face tanner in the traditional tanning bed. High pressure lamps use quartz glass, and as such do not filter UVC. Because UVC can be deadly, a special dichroic filter glass (usually purple) is required that will filter out the UVC and UVB. The goal with high pressure tanning bulbs is to produce a high amount of UVA only. Unfiltered light from a high pressure lamp is rich in UVC used in germicidal lamps, for water purification, but it damages human skin.
The contents of a high pressure lamp are inert gas (such as argon) and mercury. There are no phosphors used, and the mercury is clearly visible if it is not in a gaseous state. During installation, even a small amount of oil from fingertips can cause the quartz envelope to fail in operation. Most commercial replacement bulbs come with a special pocket wipe, usually containing alcohol, to clean the bulb in case it is accidentally touched during installation. Because the bulb contains mercury, great care should be used if a bulb is broken, to prevent accidental contact or vapor exposure.
While studying the beneficial effects of ultraviolet light on athletes, German scientist Friedrich Wolff noticed an interesting side effect - tanned skin. Realizing the appeal of a beautiful tan, Wolff founded the indoor tanning industry. His research led to development of indoor tanning equipment and lamp technology. Called "the father of indoor tanning," Wolff brought his European technology to the United States in 1978. He set the standard for the industry with specialized lamps and a reflector system that was ideally suited to indoor tanning. Today, the company operates in North America and Western Europe, and has patent licensees in Belgium, Canada, Germany, Sweden, Switzerland and the United States.
Low pressure lamps resemble the common fluorescent lamp used in offices everywhere (see image at top of page). The lamps are sized by using common codes for fluorescent lamps such as F71T12BL50BP In this example, the F71 denotes the length, nominally 71 inches. The T12 section refers to the diameter of the lamp in 1/8 inch increments, making a T12 lamp 1.5 inches in diameter. The other numbers are optional, but commonly used, with the BL standing for a blue phosphor, the 50 indicating a 5% UVB (95% UVA) rating, and the BP indicating bi-pin ends, which all F71 lamps have. Lamps with the RDC code have Recessed Dual Connector (or Recessed Dual Contact) lamp ends are typically found in F73 and more rarely F72 and F74 sizes. The RDC connector is actually a plastic piece that fits over the two bi-pins and allows the lamps to be installed in telescopic lamp ends. These are less common as the lamp end parts are significantly more expensive for the tanning bed manufacturer to use.
Like all fluorescent lamps, low pressure tanning lamps have a ballast to start the lamps and limit the flow of current. The plasma of excited mercury atoms inside the lamp emits ultraviolet light directly. The lamps are coated on the inside with special phosphors. Unlike high pressure lamps, the glass that is used in low pressure lamps filters out all UVC. Once the plasma is fully formed, the plasma literally strips away the outer electrons from the mercury; when these electrons return to a lower energy level, visible and ultraviolet light is emitted. Some of the short-wave ultraviolet excites the phosphors, which then emits photons in the proper spectrum for tanning.
The first tanning lamps were discovered by accident in 1903 by a German company called Heraeus who were developing lighting systems for the home and for industrial usage. These lamps were of the high-pressure metal halide variety. They discovered that the lamp that was developed for visible light purposes also emitted ultra-violet light. In the 1920s and 1930s they first started to market and sell single lamp, self standing tanning/wellness devices. The first high-pressure tanning beds incorporating more than a single high-pressure lamp were manufactured in the mid to late seventies by companies such as Ultrabronz and JK Ergoline and in the 1980s the first high-pressure units were exported to the United States.
In the older style (but still most popular) "choke ballast", each end of the lamp has its own cathode and anode, however, once the lamp has started, the plasma flows from one end of the lamp to the other, with each end acting as a single cathode or anode. The starter is a plasma switch itself, and temporarily connects the cathode on one end of the lamp to the anode on the other end of the lamp, causing the lamp ends to heat up quickly, or "preheat". Many F71 lamps are still called "pre-heat bi-pin" for this reason.
Newer electronic systems work differently and always treat one end of the lamp as a cathode and one end as an anode. Whereas the choke style always works at 230 V AC at 60 Hz (220-240 V AC/50 Hz in Europe), newer electronics work very differently. This includes magnetic, pure solid state, and high frequency ballasts. These new ballasts operate at voltages up to 600 V AC, and at 20,000 Hz, with some high frequency ballasts operating as high as 100,000 Hz or higher. This allows the ballast to energize the lamp with more than raw power, and instead operates using a combination of electrical force and induction. This allows a 100 watt lamp to fully light with as little as 65 watts.
The advantage of the newer electronics is that they use less electricity, cost less to operate, and operate at temperatures that are well below choke ballasts. Some new electronic ballasts get as little as 10 °F (5.6 °C) hotter than ambient temperature, even after running for an extended period.
The disadvantage of the newer electronics is price. It can cost 3 to 5 times more per lamp to use electronic ballasts than traditional choke ballasts, which is why choke ballasts are still used in the majority of new tanning systems. Another disadvantage of the older style choke ballast is they are designed for European electricity, and require incoming voltage in the range of 220 V AC and 230 V AC. Most US homes have 240 V service and businesses use 208 V three-phase service that requires these beds to use a buck-boost transformer in order to receive the proper voltage. Too low a voltage will result in the lamp starter not letting the lamp ignite (or at the least, very slowly) whereas too high a voltage can lead to premature failure in the starters and lamps. The average cost of these transformers is $200 to $250. While this makes the newer electronics cost about the same for the typical tanning bed, buckboost transformers are usually sold separately, so the total cost is not always obvious to the consumer at first glance.
Tanning lamps come in several configurations which are considered standards within the industry,including:
The power listing for lamps is not absolute, as you can drive a lamp with less power than listed if you use certain solid state ballasts. You can also use a 160 W lamp with a 100 W ballast, although there are no advantages to this. Using a 100 W lamp with a 160 W ballast, however, can lead to quick failure as the cathode/anode of some 100 W lamps can not take the extra power. The lamps will operate at any frequency (50 Hz to 120,000 Hz or higher). However, the ballasts and other electrical systems on the tanning bed are sensitive to frequency.
Like all fluorescent lamps, the low pressure lamps will burn for a long period of time. They will, however, lose their ability to produce a reasonable amount of UV after a short while. Typical lifespans for low pressure lamps are from 300 to 1600 hours of actual use although they may actually light (and produce very little UV) for as much as 5000 hours. High pressure lamps range from 300 to 1000 hours, and should be replaced when they have reached their maximum life to prevent any possible damage to the ballast, although this is very rare. Lamp manufacturers generally rate the "life" of the lamp to be the period of time that the lamp will continue to emit at least 70% to 80% of the initial UV.
In addition to standard lamps, there are also lamps with reflectors built inside. This is accomplished by taking the raw glass before any phosphor is used and pouring a white, opaque, highly reflective chemical on the inside of the lamp. This is done only on a certain percentage of the lamp, such as 210 degrees or 180 degrees, so that the remaining lamp is NOT coated. After this coating has dried or has been treated to ensure it will stick to the surface of the glass (using heat, for example) the lamp is coated on the inside with the phospor blend as usual. Anywhere from 3 to 5 different chemicals are typically used in a blend, with the actual proportions and chemicals closely guarded as trade secrets.
The 100 watt version of a reflector lamp is typically called a RUVA (Reflector UVA) or less commonly HO-R (High Output - Reflector). The 160 watt version are called VHO-R (Very High Output - Reflector). Although many people use the name VHR to describe 160 W reflector lamps, it is actually a registered trademark of Cosmedico, Ltd, and can only be legally used when describing their products. There are many other variations of low pressure tanning lamps including 26 watt, 80 watt, and 200 watt to name a few.
This is one of the most confusing aspects of tanning lamps in the US, as lamps are not rated for their total output, but rather their ratio of UVA to UVB. Most people would be led to believe that a 6.5% lamp is stronger than a 5% lamp, while both lamps might have the same total UV output (or the 5% could even be stronger across the spectrum). As such, the rating on lamps only tells you the relative amount of UV, making a 5% lamp really a lamp whose UV spectrum is 5% UVB and 95% UVA. There are no accepted published numbers for rating the overall power for lamps, except the TE (time exposure), which is almost as useless for making comparisons.
The TE isn't generally published, although it is usually available from the lamp manufacturer on request. Because the U.S. Food and Drug Administration (FDA) biases tests against UVB, the TE may make a weaker lamp appear stronger by having more UVB. Furthermore although tanning beds are rated with exposure times, tanning lamps are not because beds can vary widely as to how a given lamp affects the user, making it difficult or impossible to compare the total UV output of different low pressure lamps.
The UVB to UVA ratio percentage is considered an outdated form of measuring a lamp's output and Wolff now lists actual UVA, UVB and total UV flux powers. This is the best way of measuring a low pressure and high-pressure lamp. Actual Wolff lamp outputs are listed here If you are purchasing a lamp from any manufacturer always ask for actual flux power output, as UVA to UVB ratios tell very little.
Tanning lamps are virtually maintenance free, but must be kept clean as UV can easily be blocked by dust drawn in from the cooling system (or from improperly cleaned acrylics shields). Most manufacturers recommend wiping the lamps and other internals clean every 200 to 300 hours of operation. Most salons will replace their tanning lamps once per year, while home tanning bed owners can expect 3 to 5 years of use. This depends solely on the number of hours the lamps have been used and the rated life of the lamp, which varies from model to model.
High pressure lamps must be handled very carefully, as any oil from the skin that is left on the bulb can cause the bulb to overheat and lead to early failure. The filter glass must also be handled carefully as it is extremely fragile by its nature. These should only be cleaned with special chemicals designed for this purpose. Operating any tanning equipment that uses high pressure bulbs without the special filter glass is extremely dangerous, and illegal in a salon, due to the high amount of UVC generated in the bulbs.
The amount of UV that is generated from a low pressure lamp is highly dependent on the temperature in the tanning unit. As a rule, tanning lamps produce the highest amount of ultraviolet light when this temperature is between 90 and 110 degrees Fahrenheit (32 to 43 degrees Celsius). As the temperature moves away from this range, the amount of UV produced is reduced. Cooling systems for tanning equipment are usually designed to maintain a range of temperature instead of providing maximum airflow for this reason. Higher temperatures will also reduce the expected life of the tanning lamp. This is why it is important to perform regular maintenance, including checking cooling fans and insuring that vent holes are not blocked. The owners manual for the tanning equipment is the best source for maintenance schedules and methods.
In addition to their use in tanning beds and booths, tanning lamps (or other UV producing lamps) are used for the treatment of psoriasis, eczema, and to cure or age wood used to build violins, guitars and other musical instruments. Water purification and medical instrument sterilization are both done using UVC, which low pressure tanning lamps do not emit, and which is filtered from high pressure lamps in tanning devices.
All fluorescent lamps contain mercury, and at this time, no suitable replacement has been found. Many US states have banned disposal of lamps containing mercury, and have established regulations requiring that lamps containing mercury are identified as such. This has not caused problems for manufacturers, however, as lamps are not produced locally, and often not in the US. There have been several efforts to label all lamps that contain mercury with a universally accepted symbol, Hg. Old lamps should be handled as would be any hazardous material in your locality, and persons should take special precautions when dealing with broken lamps to avoid contact with mercury. This is particularly true for pregnant women. These laws and guidelines are not unique to tanning lamps, and apply to all fluorescent lamps, other lamps that contain mercury, as well as other products that contain mercury with the exception of pharmaceuticals. Proper disposal or recycling will prevent the small mercury content of the lamps from entering the environment.
A germicidal lamp is a special type of lamp which produces ultraviolet light (UVC). This short-wave ultraviolet light disrupts DNA base pairing causing thymine-thymine dimers leading to death of bacteria on exposed surfaces. It can also be used to produce ozone for water disinfection.
There are two common types available:
Low-pressure lamps are very similar to a fluorescent lamp, with a wavelength of 253.7 nm.
The most common form of germicidal lamp looks similar to an ordinary fluorescent lamp but the tube contains no fluorescent phosphor. In addition, rather than being made of ordinary borosilicate glass, the tube is made of fused quartz. These two changes combine to allow the 253.7 nm ultraviolet light produced by the mercury arc to pass out of the lamp unmodified (whereas, in common fluorescent lamps, it causes the phosphor to fluoresce, producing visible light). Germicidal lamps still produce a small amount of visible light due to other mercury radiation bands.
An older design looks like an incandescent lamp but with the envelope containing a few droplets of mercury. In this design, the incandescent filament heats the mercury, producing a vapor which eventually allows an arc to be struck, short circuiting the incandescent filament.
Medium-pressure lamps are much more similar to HID lamps than fluorescent lamps.
These lamps radiate a broad-band UV-C radiation, rather than a single line. They are widely used in industrial water treatment, because they are very intense radiation sources. They are as efficient as low-pressure lamps. Medium-pressure lamps produces very bright bluish white light.
As with all gas discharge lamps, all of the styles of germicidal lamps exhibit negative resistance and require the use of an external ballast to regulate the current flow through them. The older lamps that resembled an incandescent lamp were often operated in series with an ordinary 40 W incandescent "appliance" lamp; the incandescent lamp acted as the ballast for the germicidal lamp.
Germicidal lamps are used to sterilize workspaces and tools used in biology laboratories and medical facilities. If the quartz envelope transmits wavelengths shorter than 253.7nm, they can also be used wherever ozone is desired, for example, in the sanitizing systems of hot tubs and aquariums. They are also used by geologists to provoke fluorescence in mineral samples, aiding in their identification. In this application, the light produced by the lamp is usually filtered to remove as much visible light as possible, leaving just the UV light.
The light produced by germicidal lamps is also used to erase EPROMs; the ultraviolet photons are sufficiently energetic to allow the electrons trapped on the transistors' floating gates to tunnel through the gate insulation, eventually removing the stored charge that represents binary ones and zeroes.
Germicidal lamps are also used in waste water treatment in order to kill microorganisms.
Short-wave UV light is harmful to humans. In addition to causing sunburn and (over time) skin cancer, this light can produce extremely painful inflammation of the cornea of the eye, which may lead to temporary or permanent vision impairment. It can also damage the retina of the eye. For this reason, the light produced by a germicidal lamp must be carefully shielded against both direct viewing and reflections and dispersed light that might be viewed.
"Arc lamp" or "arc light" is the general term for a class of lamps that produce light by an electric arc (also called a voltaic arc). The lamp consists of two electrodes, typically made of tungsten, which are separated by a gas. The type of lamp is often named by the gas contained in the bulb; including neon, argon, xenon, krypton, sodium, metal halide, and mercury. The common fluorescent lamp is actually a low-pressure mercury arc lamp.
The electric arc in an arc lamp consists of gas, which is initially ionized by a high voltage and therefore becomes electrically conductive. To start an arc lamp, a very high voltage is pulsed across the lamp to "ignite" or "strike" the arc across the gas. This requires an electrical circuit with an igniter and a ballast. The ballast is wired in series with the lamp and performs two functions.
First, when the power is first switched on, the igniter/starter (which is wired in parallel across the lamp) sets up a small current through the ballast and starter. This creates a small magnetic field within the ballast windings. A moment later the starter interrupts the current flow from the ballast, which has a high inductance and therefore tries to maintain the current flow (the ballast opposes any change in current through it); it cannot, as there is no longer a 'circuit'. As a result, a high voltage appears across the ballast momentarily - to which the lamp is connected, therefore the lamp receives this high voltage across it which 'strikes' the arc within the tube/lamp. The circuit will repeat this action until the lamp is ionized enough to sustain the arc.
When the lamp sustains the arc, the ballast performs its second function, to limit the current to that needed to operate the lamp. The lamp, ballast and igniter are rated matched to each other; these parts must be replaced with the same rating as the failed component or the lamp will not work.
The colour of the light emitted by the lamp changes as its electrical characteristics change with temperature and time. Lightning is a similar principle where the atmosphere is ionized by the high potential difference (voltage) between earth and storm clouds.
The temperature of the arc in an arc lamp can reach several thousand degrees Celsius. The outer glass envelope can reach 500 degrees Celsius, therefore before servicing one must ensure the bulb has cooled sufficiently to handle. Often, if these type of lamps are turned off or lose their power supply, one cannot restrike the lamp again for several minutes (called cold restrike lamps), some lamps (mainly fluorescent tubes/energy saving lamps) can be restruck as soon as they are turned off (called hot restrike lamp).
In popular use, the term arc lamp means carbon arc lamp only. In a carbon arc lamp, the electrodes are carbon rods in free air. To ignite the lamp, the rods are touched together, thus allowing a relatively low voltage to strike the arc. The rods are then slowly drawn apart, and electric current heats and maintains an arc across the gap. The tips of the carbon rods are heated to incandescence, creating light. The rods are slowly burnt away in use, and need to be regularly adjusted to maintain the arc. Many ingenious mechanisms were invented to effect this automatically, mostly based on solenoids. In the simplest form (which was soon superseded by more smoothly acting devices) the electrodes are mounted vertically. The current supplying the arc is passed in series through a solenoid attached to the top electrode. If the points of the electrodes are touching (as in start up) the resistance falls, the current increases and the increased pull from the solenoid draws the points apart. If the arc starts to fail the current drops and the points close up again.
The concept was first demonstrated by Sir Humphry Davy in the early 19th century (1802, 1805, 1807 and 1809 are all mentioned), using charcoal sticks and a 2000-cell battery to create an arc across a 4-inch gap. He mounted his electrodes horizontally and noted that, because of the strong convection flow of air, the arc formed the shape of an arch. He coined the term "arch lamp", which was contracted to "arc lamp" when the devices came into common usage.
There were attempts to produce the lamps commercially after 1850 but the lack of a constant electricity supply thwarted efforts. Thus electrical engineers began focusing on the problem of improving Faraday's dynamo. The concept was improved upon by a number of people including William Staite and Charles F. Brush. It was not until the 1870s that lamps such as the Yablochkov candle were more commonly seen. In 1877, the Franklin Institute conducted a comparative test of dynamo systems. The one developed by Brush performed best, and Brush immediately applied his improved dynamo to arc-lighting. Brush's lamps were installed on Public Square in Cleveland, Ohio, on April 29, 1879. In 1880, Brush established the Brush Electric Company.
The harsh and brilliant light was found most suitable for public areas, being around 200 times more powerful than contemporary filament lamps.
Usage of Brush electric arc lights in 1881 was reported as:
There were three major advances in the 1880s:
In the US, patent protection of arc-lighting systems and improved dynamos proved difficult and as a result the arc-lighting industry became highly competitive. Brush's principal competition was from the team of Elihu Thomson and Edwin J. Houston. These two had formed the American Electric Company in 1880, but it was soon bought up by Charles A. Coffin, moved to Lynn, Massachusetts, and renamed the Thomson-Houston Electric Company. Thomson remained, though, the principal inventive genius behind the company patenting improvements to the lighting system. Under the leadership of Thomson-Houston's patent attorney, Frederick P. Fish, the company protected its new patent rights. Coffin's management also led the company towards an aggressive policy of buy-outs and mergers with competitors. Both strategies reduced competition in the electrical lighting manufacturing industry. By 1890, the Thomson-Houston company was the dominant electrical manufacturing company in the US (Noble, 6-10). Nikola Tesla received U.S. Patent 447920, "Method of Operating Arc-Lamps" (March 10, 1891), that describes a 10,000 cycles per second alternator to suppress the disagreeable sound of power-frequency harmonics produced by arc lamps operating on frequencies within the range of human hearing.
Around the turn of the century arc-lighting systems were in decline, but Thomson-Houston controlled key patents to urban lighting systems. This control slowed the expansion of incandescent lighting systems being developed by Thomas Edison's Edison General Electric Company. Conversely, Edison's control of direct current distribution and generating machinery patents blocked further expansion of Thomson-Houston. The roadblock to expansion was removed when the two companies merged in 1892 to form the General Electric Company (Noble, 6-10).
Arc lamps were used in some early motion-picture studios to illuminate interior shots. One problem was that they produce such a high level of ultra-violet light that many actors needed to wear sunglasses when off camera to relieve sore eyes resulting from the ultra-violet light. The problem was solved by adding a sheet of ordinary window glass in front of the lamp, blocking the ultra-violet. By the dawn of the "talkies", arc lamps had been replaced in film studios with other types of lights. In 1915, Elmer Ambrose Sperry began manufacturing his invention of a high-intensity carbon arc searchlight. These were used aboard warships of all navies during the 20th century for signaling and illuminating enemies. In the 1920s carbon arc lamps were sold as family health products, a substitute for natural sunlight.
Arc lamps were soon superseded by more efficient and longer-lasting filament lamps in most roles, remaining in only certain niche applications such as cinema projection and searchlights, but even in these applications conventional carbon arc lamps are being pushed into obsolescence by xenon arc lamps.
A Yablochkov candle (sometimes electric candle) is a type of electric carbon arc lamp, invented in 1876 by Pavel Yablochkov.
A Yablochkov candle consists of a sandwich of two long carbon blocks, approximately 6 by 12 millimetres in cross-section, separated by a block of inert material such as plaster of paris or kaolin. There is a small piece of fuse wire or carbon paste linking the two carbon blocks at the top end. The assembly is mounted vertically into a suitable insulated holder.
On application of the electric supply, the fuse wire 'blows' and strikes the arc. The arc then continues to burn, gradually consuming the carbon electrodes (and the intervening plaster) as it does so. The first candles were powered by a Gramme machine.
On disconnecting the supply, the arc extinguishes. It cannot be restarted, as there is now no fuse wire between the electrodes. Once switched off or consumed, the candle must be replaced. Electrodes last about two hours.
The advantage of the design over other carbon arc designs is that it removes the need for a mechanical regulator to maintain the appropriate distance between the carbon blocks to sustain the arc.
It was first demonstrated as street and theatre illumination during the Paris Exhibition of 1878, notably on the Avenue de l'Opéra. The candles were enclosed in globes of enamelled glass, with four to twelve candles in each connected in series.
Carbide lamps, properly known as acetylene gas lamps, are simple lamps that produce and burn acetylene (C2H2) which is created by the reaction of calcium carbide (CaC2) with water.
Acetylene gas lamps were used to illuminate buildings, as lighthouse beacons, and as headlights on motor-cars and bicycles. Portable carbide lamps, worn on the hat or carried by hand, were widely used in mining in the early twentieth century. They are still employed by cavers, hunters, and cataphiles.
The conventional process of producing acetylene in a lamp involves putting the calcium carbide in the lower chamber (the generator). The upper reservoir is then filled with water. A threaded valve or other mechanism is used to control the rate at which the water is allowed to drip onto the chamber containing the calcium carbide. By controlling the rate of water flow, the production of acetylene gas is controlled. This, in turn, controls the flow rate of the gas and the size of the flame at the burner, (and thus the amount of light it produces).
This type of lamp generally has a reflector behind the flame to help project the light forward. An acetylene gas powered lamp produces a surprisingly bright, broad light. Many cavers prefer this type of unfocused light as it improves peripheral vision in the complete dark. The reaction of carbide with water produces a fair amount of heat independent of the flame. In cold caves, carbide lamp users can use this heat to help stave off hypothermia.
When all of the carbide in a lamp has been reacted, the carbide chamber contains a wet paste of slaked lime (calcium hydroxide). This is emptied into a waste bag and the chamber can be refilled. The residue is basic and toxic to animals so should not be deposited in locations where animals may consume it. However, over time the hydroxide will react with atmospheric carbon dioxide to form calcium carbonate, which is non-toxic.
Small carbide lamps called "carbide candles" are used for blackening rifle sights to reduce glare. These "candles" are used due to the sooty flame produced by acetylene.
Early caving enthusiasts, not yet having the advantage of light-weight electrical illumination, introduced the carbide lamp to their hobby. While increasingly replaced by more modern choices, a substantial percentage of cavers still use this method.
In cave surveys, carbide lamps are favored for the lead or "point" surveyor, who must identify suitable points in the cave to designate as survey stations. The sooty carbide flame may be used to harmlessly mark cave walls with a nontoxic and removable station label. Especially favored for this purpose are all-brass lamps or lamps made with no ferromagnetic metals, as these lamps do not deflect the needles of a magnetic compass, which is typically read while brightly illuminated from above using the caver's lamp.
Apart from their use as cave surveying tools, many cavers favor carbide lamps for their durability and quality of illumination. They were once favored for their relative illumination per mass of fuel compared to battery powered devices, but this advantage was largely negated with the advent of high-intensity LED illumination.
The acetylene producing reaction is exothermic, which means that the lamp's reactor vessel will become quite warm to the touch; this can be used to warm the hands. The heat from the flame can also be used to warm the body by allowing the exhaust gases to flow under a shirt pulled out from the body: such a configuration is referred to as a "Palmer furnace", after geologist Arthur Palmer.
Acetylene lamps were also used on riverboats for night navigation. The National Museum of Australia has a lamp made in about 1910 that was used on board PS Enterprise, a paddle steamer which has been restored to working order, and is also in its collection.
In 1892, Thomas Willson discovered an economically efficient process for creating calcium carbide, which is used in the production of acetylene gas. In 1895, he sold his patent to Union Carbide. Domestic lighting with acetylene gas was introduced circa 1894 and bicycle lamps from 1896.
The first carbide mining lamp developed in the United States was patented in New York on August 28, 1900 by Frederick Baldwin. Another early lamp design is shown in a patent from Duluth, Minnesota on October 21, 1902. In the late 1900s, Gustaf Dalén invented the Dalén light. This combined two of Dalén's previous inventions: the substrate Agamassan and the Sun valve. Inventions and improvements to carbide lamps continued for decades. On March 10, 1925 Andrew Prader of Spokane, Washington was granted a United States Patent, number 1,528,848 for certain new and useful improvements for Acetylene Lamps.
After carbide lamps were implicated in an Illinois coal-seam methane gas explosion that killed 54 miners, the 1932 Moweaqua Coal Mine disaster, the use of carbide lamps was phased out in United States coal mines. They continued in use in the coal pits of other countries, notably Russia and Ukraine.
The Argand lamp was invented and patented in 1780 by Aimé Argand. It greatly improved on the home lighting oil lamp of the day by producing a light equivalent to about 6 to 10 candles.
The Argand lamp had a tubular wick mounted between a pair of concentric cylindrical metal tubes so that air is channeled through the center of the wick, as well as outside it. A cylindrical chimney, in early models made of ground glass and sometimes tinted, surrounded the wick, steadying the flame and improving the flow of air. It used a supply of good liquid oil, either whale oil, colza or other vegetable oil as the fuel. This was supplied by gravity feed from a reservoir mounted above the burner. Aside from the improvement in brightness, the more complete combustion of the wick and oil required much less frequent snuffing (trimming) of the wick.
The Argand lamp quickly displaced all other varieties of oil lamps and was manufactured in a great variety of decorative forms. They were more costly than the primitive oil lamps of former times because of their increased complexity, so they were adopted first by the well-to-do, but soon spread to the middle class and eventually the less well-off as well. It was the lamp of choice until about 1850 when kerosene lamps were introduced. Kerosene was cheaper than vegetable oil, it produced a whiter flame, and as a liquid of low viscosity it could easily travel up a wick eliminating the need for complicated mechanisms to feed the fuel to the burner.
In France, they are known as "Quinquets" after Antoine-Arnoult Quinquet, a pharmacist in Paris, who stole the idea from Argand and popularized it in France. He is sometimes credited, in France, with the addition of the glass chimney to the lamp.
A disadvantage of the original Argand arrangement was that the oil reservoir needed to be above the level of the burner because the heavy, sticky vegetable oil would not rise far up the wick. This made the lamps top heavy and cast a shadow in one direction away from the lamp's flame. The Carcel lamp of 1800 and Franchot's moderator lamp of 1836 sought to overcome these problems.
Electroluminescent wire (often abbreviated to EL wire) is a thin copper wire coated in a phosphor which glows when an alternating current is applied to it. It can be used in a wide variety of applications- vehicle and/or structure decoration, safety and emergency lighting, toys, clothing etc - much as rope light or Christmas lights are often used. Unlike these types of strand lights, EL wire is not a series of points but produces a 360 degree unbroken line of visible light. Its thin diameter makes it flexible and ideal for use in a variety of applications such as clothing or costumes.
EL wire's construction consists of five major components. First is a solid-copper wire core, coated with phosphor. A very fine wire is spiral-wound around the phosphor-coated copper core. This fine wire is electrically isolated from the copper core. Surrounding this 'sandwich' of copper core, phosphor, and fine copper wire is a clear PVC sleeve. Finally, surrounding this thin, clear PVC sleeve is another clear, colored translucent, or fluorescent PVC sleeve.
An electric potential of approximately 90 - 120 volts at about 1000 Hz is applied between the copper core wire and the fine wire that surrounds the copper core. The wire can be modelled as a coaxial capacitor with about 1 nF of capacitance per foot, and the rapid charging and discharging of this capacitor excites the phosphor to emit light. The colors of light that can be produced efficiently by phosphors are limited, so many types of wire use an additional fluorescent organic dye in the clear PVC sleeve to produce the final result. These organic dyes produce colors like red and purple when excited by the blue-green light of the core.
A resonant oscillator is typically used to generate the high voltage drive signal. Because of the capacitance load of the EL wire, using an inductive (coiled) transformer makes the driver a tuned LC oscillator, and therefore very efficient. The efficiency of EL wire is very high, and thus a few hundred feet of EL wire can be driven by AA batteries for several hours.
Chemiluminescence (sometimes "chemoluminescence") is the emission of light with limited emission of heat (luminescence), as the result of a chemical reaction. Given reactants A and B, with an excited intermediate ◊,
For example, if [A] is luminol and [B] is hydrogen peroxide in the presence of a suitable catalyst we have:
The decay of this excited state[◊] to a lower energy level causes light emission. In theory, one photon of light should be given off for each molecule of reactant. This is equivalent to Avogadro's number of photons per mole of reactant. In actual practice, non-enzymatic reactions seldom exceed 1% QC, quantum efficiency.
In a chemical reaction, reactants collide to form a transition state, the enthalpic maximum in a reaction coordinate diagram, which proceeds to the product. Normally, reactants form products of lesser chemical energy. The difference in energy between reactants and products, represented as ΔHrxn, is turned into heat, physically realized as excitations in the vibrational state of the normal modes of the product. Since vibrational energy is generally much greater than the thermal agitation, it is rapidly dispersed into the solvent through solvent molecules' rotation and translation. This is how exothermic reactions make their solutions hotter. In a chemiluminescent reaction, the direct product of a reaction is delivered in an excited electronic state, which then decays into an electronic ground state through either fluorescence or phosphorescence, depending on the spin state of the electronic excited state formed. This is possible because chemical bond formation can occur on a timescale faster than electronic transitions, and therefore can result in discrete products in excited electronic states.
Chemiluminescence differs from fluorescence in that the electronic excited state is derived from the product of a chemical reaction rather than the more typical way of creating electronic excited states, namely absorption. It is the antithesis of a photochemical reaction, in which light is used to drive an endothermic chemical reaction. Here, light is generated from a chemically exothermic reaction.
A standard example of chemiluminescence in the laboratory setting is the luminol test. Here, blood is indicated by luminescence upon contact with iron in hemoglobin. When chemiluminescence takes place in living organisms, the phenomenon is called bioluminescence. A lightstick emits light by chemiluminescence.
Enhanced chemiluminescence is a common technique for a variety of detection assays in biology. A horseradish peroxidase enzyme (HRP) is tethered to the molecule of interest (usually through labeling an immunoglobulin that specifically recognizes the molecule). This enzyme complex, then catalyzes the conversion of the enhanced chemiluminescent substrate into a sensitized reagent in the vicinity of the molecule of interest, which on further oxidation by hydrogen peroxide, produces a triplet (excited) carbonyl which emits light when it decays to the singlet carbonyl. Enhanced chemiluminescence allows detection of minute quantities of a biomolecule. Proteins can be detected down to femtomole quantities, well below the detection limit for most assay systems.
Radioluminescence is the phenomenon by which luminescence is produced in a material by the bombardment of ionizing radiation such as beta particles.
Tritium is used as a source of beta particles in a large variety of applications where electricity is not available for illumination. For example, gun sights and emergency exit signs.
Historically a mixture of radium and copper-doped zinc sulfide was used to paint instrument dials giving a greenish glow. Phosphors containing copper doped zinc sulfide (ZnS:Cu), yielding blue-green light and copper and magnesium doped zinc sulfide (ZnS:Cu,Mg), yielding yellow-orange light are also used. Radium based luminescent paint is no longer used due to the radiation hazard posed to those manufacturing the dials. These phosphors are not suitable for use in layers thicker than 25 mg/cm², as the self-absorption of the light then becomes a problem. Furthermore, zinc sulfide undergoes degradation of its crystal lattice structure, leading to gradual loss of brightness significantly faster than the depletion of radium.
ZnS:Ag coated spinthariscope screens were used by Ernest Rutherford in his experiments discovering atomic nucleus.
Radioluminescence occurs when an incoming radiation particle collides with an atom or molecule, exciting an orbital electron to a higher energy level. The electron then returns to its ground energy level by emitting the extra energy as a photon of light.
A glow stick is a single-use translucent plastic tube containing isolated substances which when combined make light through a chemical reaction-induced chemiluminescence which does not require an electrical power source. Although the glow stick is often used for recreation, it may also be relied upon for light during important military, police and fire, or EMS operations.
Cyalume was invented by Michael M. Rauhut, David Iba Sr, Robert W. Sombathy and Laszlo J. Bollyky of American Cyanamid, based on work by Edwin A. Chandross of Bell Labs in conjunction with Richard D. Sokolowski of Eh.M Labs. Other early work on chemiluminescence was carried out at the same time, by researchers under Herbert Richter at China Lake Naval Weapons Center.
There are several US patents for "glow stick" type devices by various inventors. Most of these are assigned to the US Navy. The earliest patent lists Bernard Dubrow, and Eugene Daniel Guth as having invented a Packaged Chemiluminescent Material in June 1965 (Patent 3,774,022). In October 1973, Clarence W. Gilliam, David Iba Sr., and Thomas N. Hall were registered as inventors of the Chemical Lighting Device (Patent 3,764,796). In June, 1974 a patent for a Chemiluminescent Device was issued with Herbert P. Richter and Ruth E. Tedrick listed as the inventors (Patent 3,819,925).
In January 1976, a patent was issued for the Chemiluminescent Signal Device with Vincent J. Esposito, Steven M. Little, and John H. Lyons listed as the inventors (Patent 3,933,118). This patent recommended a single glass ampoule that is suspended in a second substance, that when broken and mixed together provide the chemiluminescent light. The design also included a stand for the signal device so that it could be thrown from a moving vehicle and remain standing in an upright position on the road. The idea was that this would replace traditional emergency roadside flares and would be superior since it was not a fire hazard, would be easier and safer to deploy, and would not be made ineffective if struck by passing vehicles. This design with its single glass ampoule inside a plastic tube filled with a second substance that when bent breaks the glass and then is shaken to mix the substances most closely resembles the typical glow stick sold today.
In December, 1977 a patent was issued for a Chemical Light Device with Richard Taylor Van Zandt as the inventor (Patent 4,064,428). This design improved upon the previous designs by adding a steel ball inside the plastic tube that when shaken would break the glass ampoule.
Glow-sticks are used for many purposes. They are waterproof, do not use batteries, generate negligible heat, are inexpensive, and are reasonably disposable. They can tolerate high pressures, such as those found underwater. They are used as light sources and light markers by military forces, campers, and recreational divers doing night diving. Glow sticks are considered the only kind of light source that is ideal safe for use immediately following an earthquake, hurricane, tornado, or other catastrophic emergency situation due to the fact that they do not use any kind of electricity to work and do not create any danger of sparking.
Glowsticking is the use of glow sticks in dancing. This is one of their most widely known uses in popular culture as they are frequently used for entertainment at parties (particularly raves), concerts and dance clubs. They are carried by marching band conductors for night-time performances; furthermore, in Hong Kong glow sticks are widely used during the annual Mid-Autumn Festival, and in Iceland they're commonly seen during New Year's Eve. Glow sticks carried by Trick-or-Treaters on Halloween neatly serve multiple functions as toys, readily visible and unusual night-time warnings to motorists, and luminous markings which enable parents to keep their brightly color-coded children in sight. Yet another aesthetic usage is for balloon-carried light effects. Glow sticks are also used to create special effects in low light photography and film.
The Guinness Book of Records says the world's biggest glow stick, 8 ft 4 in tall, was built and illuminated at the opening ceremony of the second Bang Face Weekender at a holiday park in Camber Sands, East Sussex, England, on April 24, 2009.
It is a common belief that glow sticks may be placed in a freezer to slow the chemical reaction, allowing the same sticks to be kept for two or three night's activity. The cold induces a solid-state to the mixture and slows down the photon release. In reverse, microwaving or running hot water over them speeds up the photon release and makes them brighter, but also diminishes the life of the glow stick. This however usually depends on the specific composition of chemicals in the particular glow stick at hand.
Glow sticks give off light when two solutions are allowed to mix. The sticks consist of a small fragile container within a flexible outer container. Each container holds one of the two solutions. When the outer container is bent, it breaks the inner container, releasing the first solution into the second solution. After breaking, the tube is shaken to mix the two components. Usually to activate this reaction, you simply bend the glow stick.
Glow sticks contain hydrogen peroxide, and phenol is produced as a by-product. It is advisable to keep the mixture away from skin and to prevent accidental ingestion if the glow stick case splits or breaks. If spilled on skin the chemicals could cause slight skin irritation, swelling, or, in extreme circumstances, vomiting and nausea. Some of the chemicals used in older glow sticks were thought to potentially be carcinogens. The sensitizers used are polynuclear aromatic hydrocarbons, a class of compounds known for their carcinogenity.
The glow stick contains two chemicals and a suitable fluorescent dye (sensitizer, or fluorophor). The chemicals in the glass vial are a mixture of the dye and diphenyl oxalate. The chemical inside the plastic tube is hydrogen peroxide. By mixing the peroxide with the phenyl oxalate ester, a chemical reaction takes place; the ester is oxidized, yielding two molecules of phenol and one molecule of peroxyacid ester (1,2-dioxetanedione). The peroxyacid decomposes spontaneously to carbon dioxide, releasing energy that excites the dye, which then relaxes by releasing a photon. The wavelength of the photon—the color of the emitted light—depends on the structure of the dye. The decomposition is a reverse [2 + 2] cycloaddition, which is a forbidden transition; so the reaction cannot release its energy as heat, but