Three kinds of headlight
| Type | How it makes light | Replacing it |
|---|---|---|
| Halogen | A heated filament inside a quartz capsule filled with halogen gas | Replaceable bulb; often an owner job |
| HID (xenon) | An electric arc through gas, driven by a high-voltage ballast | Replaceable bulb, but high voltage; often a shop job |
| LED | Light-emitting diodes on a circuit board | Often built into the lamp; the whole unit may need replacing |
Bulb codes
Replaceable bulbs use standard codes that describe the base, shape and power, such as H11 or 9005 for many headlights. The same car can use several codes: one for low beams, one for high beams, others for fog lights, turn signals, brake lights and the license plate. The owner's manual lists them, and the code is usually printed on the old bulb's base.
Which bulbs are easy to change
Tail lights, brake lights, rear turn signals and license plate lights are often reached from inside the trunk or by removing a couple of screws. Many halogen headlight bulbs twist out from behind the lamp under the hood. On some cars, though, you have to remove the battery, the air box, a wheel arch liner or even the bumper cover to get at a headlight bulb. Check the manual first so you know what you are taking on.
Tips for changing a bulb
- Turn the lights and the car off, and let a recently used bulb cool.
- Find the bulb code and buy the exact match.
- Don't touch the glass of a halogen bulb with bare fingers. Skin oils can create hot spots that shorten its life. Hold it by the base or wear clean gloves.
- Seat the bulb fully and refit any rubber dust cover so moisture stays out.
- Test every function: low, high, signals, brake lights and hazards.
Replace headlight bulbs in pairs. Bulbs dim and change color as they age, so a new bulb on one side and an old one on the other gives uneven light, and the second old bulb is often close to failing anyway.
HID and LED lamps
High voltage. HID systems use a ballast that produces very high voltage at startup. Leave HID bulb and ballast work to a trained technician unless the manual describes an owner procedure.
Many factory LED headlights and tail lights are sealed units. When an LED section fails, the fix is usually a new lamp assembly or a repair by a specialist. That is shop work on most cars, and the lamp may need to be aimed after it is fitted.
Keep your lights road-legal
Lighting rules exist so you can see and other drivers aren't dazzled. In the United States, lamps on the road are expected to meet federal motor vehicle safety standards, and states set their own inspection rules. Plug-in LED or HID bulbs sold to retrofit halogen headlights may not be legal for road use and can scatter glare at oncoming drivers. Colored or very blue lights can also break local rules. Check with your state or local motor vehicle agency before changing the type of light your car uses.
Headlight aim
Headlights that point too high glare into oncoming cars, and ones that point too low shorten how far you can see. Aim can shift after a lamp is replaced or after minor front-end damage. A shop can check and adjust it.