High-intensity discharge lamp
From Wikipedia, the free encyclopedia
High-intensity discharge (HID) lamps include these types of electrical lamps: mercury vapor, metal halide (also HQI), high-pressure sodium, low-pressure sodium and less common, xenon short-arc lamps. 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/in.²).
Compared to fluorescent and incandescent lamps, HID lamps produce a far higher quantity of light per unit area of lamp package.
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[edit] Construction
HID lamps produce light by striking an electrical arc across tungsten electrodes housed inside a specially designed inner fused quartz or fused alumina tube. This tube is filled with both gas and metals. The gas aids in the starting of the lamps. Then, the metals produce the light once they are heated to a point of evaporation, forming a plasma.
Types of HID lamps include:
- Mercury vapor (CRI range 15-55)
- Metal halide (CRI range 65-80, ceramic MH can go to 90s)
- Low-pressure sodium (CRI 0 owing to their monochromatic light)
- High-pressure sodium (CRI range 22-75).
Mercury vapor lamps, which originally produced a bluish-green light, were the first commercially available HID lamps. Today, they are also available in a color corrected, whiter light. But they are still often being replaced by the newer, more efficient high-pressure sodium and metal halide lamps. Standard low-pressure sodium lamps have the highest efficiency of all HID lamps, but they produce a yellowish light. High-pressure sodium lamps that produce a whiter light are now available, but efficiency is somewhat sacrificed. Metal halide lamps are less efficient but produce an even whiter, more natural light. Colored metal halide lamps are also available.
[edit] Auxiliary devices
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.
[edit] Applications
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, outdoor activity areas, roadways, parking lots, and pathways. More recently, HID lamps, especially metal halide, have been used in small retail and residential environments. HID lamps have made indoor gardening practical, especially for plants that require a good deal of high intensity sunlight, like vegetables and flowers. They are also used to reproduce tropical intensity sunlight for indoor aquaria.
Some HID lamps such as Mercury Vapor Discharge produce large amounts of UV radiation and therefore need diffusers to block that radiation. In the last few years there have been several cases of faulty diffusers, causing people to suffer severe sunburn and Arc eye. Regulations may now require guarded lamps or lamps which will quickly burn out if their outer envelope is broken.
Recently, HID lamps have gained use in motor-vehicle headlamps. This application has met with mixed responses from motorists, mainly in response to the amount of glare that HID lights can cause. However, many motorists still prefer these lights as they emit a clearer, brighter, more natural appearing light than normal headlamps. They often have an automatic self-levelling system to minimise this issue and as such are usually an expensive optional extra on most cars.
HID lamps are used in high-end bicycle headlamps. They are desirable because they produce much more light than a halogen lamp of the same wattage. Halogen lights appear somewhat yellow in color; HID bicycle lights look faintly blue-violet.
HID lamps are also being used for all external lights on the Airbus A380 superjumbo airliner and on many other general aviation aircraft for landing and taxi lights.
[edit] See also
[edit] References
- Waymouth, John (1971). Electric Discharge Lamps. Cambridge, MA: The M.I.T. Press. ISBN 0-262-23048-8.
- National Highway Traffic Safety Administration. [http://www.nhtsa.gov/cars/rules/rulings/glare.html Glare from Headlamps and other Front Mounted Lamps
Federal Motor Vehicle Safety Standard...]. US Department of Transportation. Retrieved on 2006-01-23.
[edit] External links
| Lighting and Lamps
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|---|---|---|
| Incandescent: | Conventional - Halogen - Parabolic aluminized reflector (PAR) |  |
| Fluorescent: | Compact fluorescent (CFL) - Linear fluorescent - Induction lamp | |
| Gas discharge: | High-intensity discharge (HID) - Mercury-vapor - Metal-halide - Neon - Sodium vapor | |
| Electric arc: | Arc lamp - HMI - Xenon arc - Yablochkov candle | |
| Combustion: | Acetylene/Carbide - Candle - Gas lighting - Kerosene lamp - Limelight - Oil lamp - Safety lamp | |
| Other types: | Sulfur lamp - Light-emitting diode (LED) - Fiber optics - Plasma | |
