High Intensity Discharge (HID) headlamps, with their distinctive blue-white light, are now being fitted to many upmarket cars as standard equipment, and are becoming increasingly popular as an option on other models.
Unlike conventional halogen bulbs, HID lamps dispense with the filament and generate light by means of an arc between two electrodes mounted in an arc tube filled with the inert gas Xenon.
HID lamps have a number of advantages over conventional bulbs.
The light output from an HID bulb is more than double that produced by a typical halogen lamp, giving a beam that is significantly improved in both spread and range.
Furthermore, the power consumption at 35 watts represents a considerable saving over conventional lamps, which benefits MPG figures. The amount of heat produced is also reduced which allows the design of more compact headlights. And finally, the average life is more than three times that of a normal filament bulb.
Because of the risk of dazzling oncoming drivers, ECE regulations require that all cars fitted with HID headlamp systems be fitted with automatic headlamp levelling and a headlight washer system. This, together with the built in safety features required by the high (20,000+ volts) necessary to start these bulbs, means that it is not usually possible to retro fit HID lamps.