Automotive Headlamps
In 1991 "xenon headlamps" were introduced for vehicles. These are actually metal-halide lamps; the xenon gas is used only to provide some light immediately upon lamp startup, as required for safety in an automotive headlamp application. Full intensity is reached 20 to 30 seconds later once the salts of sodium and scandium are vapourised by the heat of the xenon arc. The lamp envelope is small and the arc spans only a few millimetres. An outer hard glass tube blocks the escape of ultraviolet radiation that would tend to damage plastic headlamp components. The first xenon headlamp burners contained mercury; newer types do not.
Read more about this topic: Xenon Arc Lamp