Headlights have come in several forms over the past 80 years or so. The older styles were sealed beams (left) with the filament mounted in a large glass assembly filled with an inert gas. Over the past few decades, new vehicles transitioned to composite headlamps which use a plastic lens and reflector along with a replaceable bulb (right). These still use a filament, but the gas-filled chamber was reduced to the small area around the filament. The latest headlight technology is HID (center), which uses two tungsten electrodes and the light comes in the form of an arc between the electrodes.