HID stands for High Intensity Discharge which is a term used for many types of lighting systems. Before HID lighting became popular for use in automobiles it was used in industrial and commercial applications. Street lamps, ceiling lights inside large commercial buildings and even some strobe lights are considered high intensity discharge lighting.
The technology in high intensity discharge is in some ways similar to fluorescent technology: an arc is established between two electrodes in a gas-filled tube which causes a metallic vapor to produce radiant energy. In this case, however, a combination of factors shifts the wavelength of much of this energy to within the visible range, so light is produced without any phosphors. In addition, the electrodes are only a few inches apart (at opposite ends of a sealed “arc tube”) and the gases in the tube are highly pressurized. This allows the arc to generate extremely high temperatures, causing metallic elements within the gas atmosphere to vaporize and release large amounts of visible radiant energy. There are three main types of HID lamps: mercury vapor, metal halide and sodium. The names refer to the elements that are added to the gases in the arc stream which cause each type to have somewhat different color characteristics and overall lamp efficiency.
Because of the ballast and arc technology employed by HID lighting it is more efficient than halogen automotive lighting bulbs. HID xenon lighting causes less heat, more light output and use less electricity to do it!
Today, HID xenon lighting has become a standard in automobile lighting. Aftermarket HID Conversion Kits are very popular and available in differing degrees of quality. Some vehicles even come with HID lighting from the manufacturer in both projector style housings and reflector style housings.