There is a dizzying array of car bulbs on the market, and it's easy to buy the wrong ones if you don't know what you're looking for. Check out our handy guide to arm yourself with the knowledge needed to always buy the correct type, and discover how to fit them too…
Inside your headlights you will commonly encounter three types of bulb; the dipped/main beam bulb (which many people refer to as the headlight bulb), the sidelight and, in some newer cars the indicator bulb - Most older cars have the indicator as a separate unit.
New cars also feature what are known as DRLs (daylight running lights) these are on all the time the engine is on and are either part of the headlight assembly, or a separate LED unit.
There are also cars with cornering lights integrated into the headlight that either come on when you turn, or the actual light swivels in relation to the wheels.
Rear lights are simpler, and incorporate the red tail lights (which may also have a stop and tail lamp in one bulb), one or two reversing lights, a fog light, indicators, and a single high-level brake light.
Different Bulb Types
Filament/Halogen
These are generally fitted to all cars prior to the advent of HIDs, and many cars still use them. They operate on the same principal as a household lightbulb with a very thin metal filament heated by an electric current.
Most car filament headlight bulbs are filled with halogen gas. These type of bulbs are cheap, long lasting and aren't difficult to change (usually!). You can get so called 'high power' bulbs, which are direct replacements for the originals.
While these may offer an improvement over the standard light, don't expect them to be a lot brighter. You may also have seen 'xenon-style' bulbs, which will emit a whiter, less yellow light.
Make sure you don't confuse these with Xenon HID lights, as they aren't the same thing. In xenon-style bulbs the halogen is replaced with xenon. Rear bulbs are most often filament style, but without the halogen filling.
Xenon HID
High Intensity Discharge (HID) bulbs are the ones most often found on newer cars that give off the whiter, brighter light (you've no doubt been dazzled by a pair at some point!).
They aren't like filament bulbs as they don't have a filament, but instead use a pair of electrodes in a glass tube. The tube is filled with xenon gas and they work on a 'gas discharge' principle.
They need what's known as a 'ballast' to operate, and this is a small electrical box which starts the lights and controls their operation. As result you cant just swap halogens for HIDs sadly. You can get aftermarket-HID kits but you can't fit them to every car, so it's probably best to stick with like-for-like, unless you've done your homework.
When Xenons near the end of their life they flicker, and the colour of the light output may also change slightly. When they do fail you'll find they cost substantially more to replace than halogen bulbs.
LED
Only on the very newest cars will you find LEDs used for the headlight bulb, but they are increasingly used for sidelights and indicators. The light output on commercially available LEDS isn't sufficient for them to be used as headlights.
You can exchange other filament bulbs for LEDs with the same fittings, but these can cause issues with some cars as their power consumption is so low that the car thinks the bulb isn't functioning and flags up a dashboard warning.
If you do intend to fit LEDs look for CANbus LEDS' as these incorporate a resistor, which mimics the effect of a regular bulb. However it's not advisable to fit CAN bus LEDs on a non-CANbus car, so you must check before fitting.
Bulb fitments
Bulbs are commonly referred to using codes such as 501, H1, H4,or H7.These should be replaced like-for-like and your handbook should tell you what bulbs you need.
Alternatively you can remove yours and check before buying. Some handbooks also show how they're replaced, but if not there may well be a Haynes guide to show you how to do it on your car.
Bulb replacement
To locate the whereabouts of the bulb that's failed turn the lights on, and see which bulb's 'out'. Note its location to make sure you replace the correct one.
Most cars have a cover on the back of the headlight that can be unclipped and the rear of the bulbs accessed. You may need to remove components to gain access (commonly the battery) but you may be lucky, and have one that can be swapped with everything in-situ.
One you've got access by removing the headlight cover (or in some cases the whole headlight) remove the connector on the back of the bulb you wish to replace.
There's likely to be a metal spring clip holding the bulb in the light so unclip this and the bulb will drop out. Some smaller lights require you to turn the fitting anti-clockwise.
When you replace any bulbs, but particularly the headlight bulbs try not to touch the glass part of the bulb. Oil from your skin can cause hotspots on the glass, which may lead to premature bulb failure.
Be warned that there are some cars where access is a nightmare, requiring wheels, or even the bumper to be removed. So make sure you know how yours fit before embarking on the job.
To gain access to the rear lights there is conventionally a flap, or hatch inside the car, which is screwed, or clipped in place. Some require you to remove the whole light cluster, and others allow you to remove the electrical circuitry from the rear with the bulbs still attached.
As with headlights it's best to arm yourself with the required knowledge before tackling the task – and always always test the bulb works before fitting the light back in the car.