Xenon high-intensity-discharge headlights employ xenon gas to produce a slightly bluish light, up to three times brighter than halogen headlights.

Technically a high-intensity-discharge (HID) light, xenon headlights are named for the inert gas they employ to amplify light produced by electricity jumping between two electrodes. HID lights don’t use a filament, as do incandescent headlights, and they tend to last two to three times longer. They also provide much more uniform intensity. Aim a set of xenon headlights at a wall, and you’ll see they define a sharp line at the top of the projected light pattern rather than the gradual fade common to conventional headlights. HID lights produce ultraviolet as well as visible light, which makes reflective highway signs glow more brilliantly.

Some drivers claim to be blinded by xenon lights’ intensity, a complaint we heard almost 20 years ago when halogen headlights came into being. Once drivers get accustomed to the bluish cast and no longer stare at them, they will probably become more accepting. Most vehicles that employ xenon headlights include a provision to ensure that they don’t blind oncoming traffic, even if the trunk is weighed down, which aims the headlights higher. Mercedes-Benz uses self-leveling technology in the lights themselves, and others have automatic leveling for the whole vehicle, which achieves the same goal. A switch on the dashboard of Infiniti’s Q45 allows the driver to select one of four headlight heights — an approach with a large margin for human error.

The blinding blue lights you see on today’s roads may, in fact, be copycats. Shortly after the first xenon lights appeared on select BMWs in 1993, aftermarket companies began cranking out blue headlight bulbs and accessory lights. The kind of person who wants to drive around with blue lights also wants to make sure you see them, and tends to aim them higher than other drivers appreciate. Most of these copycat bulbs are conventional incandescent bulbs with a blue coating or blue glass. Some include xenon gas for marketing purposes, but they still have a filament, not the gap-jumping arc. True HID lights operate on high voltages — 15,000 volts to jump the gap when first turned on and around 80 volts thereafter — so they require additional components, namely a type of transformer called a ballast. HID offroad-style accessory lights that come with a separate ballast are fairly common. Though rare, there are now true HID headlights that can be added to a vehicle not equipped with them at the factory. The examples I’ve seen are full headlight assemblies that include the ballast, not simply bulbs that fit into existing assemblies.

You’re sure to see more HID headlights in future years. Though they are currently rather expensive and often tied to premium option packages, the systems are smaller, lighter and allow for smaller headlamp assemblies — an advantage to vehicle designers and engineers alike. Though they operate on high voltage, the current they draw is actually around half that of conventional headlights, another plus. Then there’s the issue of performance; once you drive behind xenon headlights, you never want to go back.

Information for this was taken from Cars.com’s glossary, written by Joe Wiesenfelder. 

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Answered by Joe Bruzek on August 26, 2008 in How Does That Work? , I'm Just Wondering | Permalink

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