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A high-intensity discharge (HID) light 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 light.
Compared with fluorescent and incandescent lamps, HID lights 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.
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 headlights, spotlights & driving lights; and aquarium lighting.
Like fluorescent lamps, HID lights 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 lights 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 lights have been used in small retail and residential environments.
HID lights have made indoor gardening practical, particularly for plants that require high levels of direct sunlight in their natural habitat; HID lights, 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 lightss are used in LCD or DLP projection TV sets or projection displays.
Beginning in the early 1990s, HID lights have been employed in motor vehicle headlights and driving lights. This application has met with mixed responses from motorists, who appreciate the improved night time visibility from HID headlights and driving lights 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 lights 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 lights have also become common on work lights for tractors, farm equipment, many aircraft as replacements for traditional landing and taxi lights.
About HID Lights