Change Bulbs
Your car's bulbs are essential to your own visibility and to that of other road users. Defective lighting is not only dangerous, it is also against the law: it is an automatic MOT failure and, if you are stopped, can result in a fixed penalty notice (typically £100).
The different types of bulb
Each bulb has a specific function and cannot be swapped for another, even if it looks identical. Bulbs often have keyed bases to prevent mix-ups.
Decoding the bulb codes
The letter before the number indicates the technology or the base type:
Halogen
- e.g. H4, H7. The most common for main lighting.
Festoon
- e.g. C5W. Used in interior lights.
Xenon
- e.g. D2R, D1S. "R" = reflector, "S" = projector lens.
Amber
- e.g. PY21W. For the indicators.
Long life
- e.g. H7 LL. Service life x3 vs standard.
Difference between H4 and H7 bulbs
Overview of bulb types
Bulb service life
Incandescent bulbs
Variable service life: around 300 h for a P21W, 450 h for an H4, up to 1,000 h for a W3W. The LL versions offer up to three times the service life.
Xenon bulbs
Average service life of 2,000 h. Replacement calls for precautions due to the high voltage of the ballast.
LED
From 4,000 h (high power) to 30,000 h (low power). LEDs generally cannot be replaced individually.
The vehicle's exterior lighting
Changing a bulb yourself
Difficulty 1/5
In general, replacing a standard bulb is easy and takes about ten minutes. Some cases need the headlight unit or the front bumper to be removed.
Precautions
Never touch the glass of a halogen bulb with your fingers: use a lint-free cloth. Disconnect the battery before working.
Typical method
Reach the engine bay, remove the protective cover from the headlight unit, pull out the bulb holder, take out the old bulb, fit the new one, refit and check it works.
Indicative prices
From £2 for a W5W to £18 for a top-of-the-range H4. Xenon bulbs: around £90-110 (D1S/D2R).
Example: replacing a front sidelight bulb
Is it legal to replace halogens with LEDs?
In the UK, retrofit LED bulbs are not type-approved as replacements for halogen or xenon exterior lighting for road use. It is therefore not road-legal to replace exterior halogen or xenon bulbs with LEDs on a vehicle used on the public highway. Only interior lighting may be changed. If you are stopped, or at the MOT, a non-approved conversion can mean a fixed penalty and a failure.
