HID stands for high-intensity discharge, a technical term for the electric arc that produces the light. These lamps are formally known as gas-discharge burners, and produce more light for a given level of power consumption than ordinary tungsten and tungsten-halogen bulbs. Because of the increased amounts of light available from HID burners relative to halogen bulbs, HID headlamps producing a given beam pattern can be made smaller than halogen headlamps producing a comparable beam pattern. Alternatively, the larger size can be retained, in which case the xenon headlamp can produce a more robust beam pattern.
A xenon bulb contains xenon gas that produces light when heated with electricity. Some types of xenon bulbs also contain filaments like incandescents but utilize xenon to create light more efficiently. The light created by xenon bulbs is whiter than what is produced by incandescent or halogen bulbs, creating an appearance more like daylight. As long as the bulbs have a similar rating and wattage, xenon bulbs can be substituted for halogen lights.
A halogen lamp is an incandescent lamp in which a tungsten filament is sealed into a compact transparent envelope filled with an inert gas and a small amount of halogen such as iodine or bromine. The halogen cycle increases the lifetime of the bulb and prevents its darkening by redepositing tungsten from the inside of the bulb back onto the filament. The halogen lamp can operate its filament at a higher temperature than a standard gas filled lamp of similar power without loss of operating life.