Technical File

Xenon Headlights

Most car headlights use Halogen bulbs which are so named because the bulb filament is surrounded by halogen gas to give the lights long life. Many luxury and sports cars are now being fitted with high intensity discharge headlights, known as Xenon lights after the gas that is used inside the bulb.

A Xenon lamp is similar in principle to a fluorescent lamp. In both types a high-voltage electric current is used to excite the gas molecules which result in the molecules emitting light. In a fluorescent lamp the gas emits ultraviolet light, which is converted to visible light by the fluorescent coating on the inside of the glass tube.

However in an automotive Xenon lamp the excitation of the Xenon gas generates the light directly. The resultant light output has a slightly blue tinge as compared to a Halogen bulb. Xenon lights produce more light than conventional headlights and at the same time use less power. They also never require bulb replacement. But the high voltage electronics required to start the lamp currently makes them more expensive to manufacture.

Under the current law Xenon lights must have a self leveling system to prevent them from dazzling oncoming drivers. The dynamic self-leveling system uses sensors to detect the position of the front and rear axles. The sensors provide information on the compression rates of the suspension system to a small computer which controls a motor in the headlamp assembly. This reacts within milliseconds of receiving the control information and positions the headlight so that the light beam always remains at the optimum angle to avoid dazzling other drivers.

Published in The Australian 15^th September 2004

Editors Note: Although the electronics and the self leveling system make Xenon lights more expensive than Halogen lights it will not be long before State Parliaments legislate to make this new headlamp system compulsory. The argument that will be used is that it “improves safety in night driving”

There is no question that the increased light output illuminates the road very effectively. I can testify to this from the experience of driving a car that was fitted with the system at night on a country road. There was certainly no need for those extra high wattage spotlights to avoid the roo’s!