Background Information about Xenon / HID Headlamp Bulbs

The high intensity of the arc comes from metallic salts that are vapourised within the arc chamber. 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.

Automotive HID lamps are commonly called 'xenon headlamps', though they are actually metal halide lamps that contain xenon gas. The xenon gas allows the lamps to produce minimally adequate light immediately upon powerup, and accelerates the lamps' run-up time. If argon were used instead, as is commonly done in street lights and other stationary metal halide lamp applications, it would take several minutes for the lamps to reach their full output. The light from HID headlamps has a distinct bluish tint when compared with tungsten-filament headlamps.