Bulbs work by passing electric current passes through a thin filament, heating it until it produces light. Car bulbs are enclosed by glass; this prevents the oxygen in the air from reaching the hot filament, which otherwise would be destroyed rapidly by rusting of the filament.
Bulbs gradually loose performance and brightness with age and as with wiper blades, your headlamp bulbs should be replaced when they become old.
With halogen bulbs, it is essential to never touch the glass and that the glass does not get scratched or dirty. If this happens, the dirt, oil, scratch, or oil from fingers will eventually get much hotter than the rest of the bulb and will blow out.
Please choose you bulb type from the section shown.