Light Pattern of HID vs. Halogen
Road Illumination of HID vs. Halogen
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HID
HID stands for high intensity discharge, a technical term for an electric arc, or plasma, between two tungsten electrodes that produces visible light. The high intensity of the arc comes from metallic salts that are vaporized within the arc chamber. The arch chamber is a transparent fused quartz or fused alumina arc tube. These lamps are formally known as gas-discharge burners, and produce more light for a given level of power consumption than ordinary incandescent or halogen incandescent bulbs. Because of the increased amounts of light available from HID burners relative to halogen bulbs, HID headlamps can be made smaller to produce a tighter beam pattern.
Automotive HID lamps are commonly called 'xenon headlamps', though they are actually metal halide lamps that contain xenon gas. Metal halide lamps are what you see in streetlights. 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 that HID headlamps produce is very pure. One can usually recognize an automotive HID light by the bluish tint, or the distinctly white light that it produces.
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