Light Sources

     The devices popularly known as "Xenon headlamps" actually incorporate metal-halidelight sources，and are known as high-intensity discharge，or HID lamps. Unlike a halogenbulb，the HID bulb has no filament. It creates light from an electrical discharge betweentwo electrodes in a tiny quartz capsule filled with xenon gas. The lights and supportelectronics are expensive，but they should last the life of the vehicle unless physicallydamaged. It produces twice the light with less electrical input than conventional halogenbulbs.

    Light Emitting Diodes (LED)

    LEDs are the last generation and are used with increasing frequency in automotivesignaling lamps. They operate with much lower power consumption，have longer servicelives，are nearly impervious to vibration damage，and permit considerably shallowerpackaging compared to most bulb-type assemblies. LEDs also offer a significant safetyperformance benefit when employed in brake lights，for when power is applied they rise tofull intensity approximately 200 milliseconds faster than incandescent bulbs. This fast risetime not only improves the attentional conspicuity of the brake lamp，but also providesfollowing drivers with increased time in which to react to the appearance of the brake lamps.