2003-2011 Mercury Grand Marquis Driver Side Tail Light

These types of lights used to be more popular on most European vehicles, but are becoming common on other makes and models. Projector lights are lights that have a filament located at one focus of a reflector, and a round glass or heavy duty plastic condenser lens at the front of the lamp. These lenses in front of the light bulb distribute the light evenly across the front of the vehicle, and can give a larger range of visibility for the driver. The bulbs themselves are usually common Halogen bulbs that can easily be changed.

HID stands for "High Intensity Discharge". These bulbs use an electric arc rather than the glowing filament in a Halogen bulb. HID headlamp bulbs do not run on low-voltage DC current like a Halogen Bulb, so they require a ballast, which controls and regulates the flow of current. This ballast will require an ignitor to light the bulb. This is either integrated directly into the bulb or as a separate unit which is occasionally part of the ballast, similar to fluorescent bulbs in your home. In a vehicle, HID bulbs tend to be much more expensive to replace than a Halogen bulb.

HID lights can also be referred to as Xenon bulbs (though not all Xenon bulbs are HID). Some vehicle manufacturers also use Bi-Xenon headlights, headlights which use an HID low beam bulb in combination with a halogen high beam bulb.