Which interior bulbs does my car take?
The three bulb types
| Type | How to recognise it | Where it is used | LED versions |
|---|---|---|---|
| W5W wedge (T10, 501) | Small glass bulb with a flat plastic or glass base that pushes straight in; no metal cap. | Number plate lights, boot lights, footwells, glovebox, vanity mirrors, side repeaters on older cars. | See on Amazon |
| Festoon (C5W, 239, 272, 264) | A tube with a pointed metal cap at each end, held between two spring clips. | Dome and map lights, boot lights, number plate lights on many cars. Sold by length: about 31, 36, 39, 41 and 42 mm are the common sizes. | See on Amazon |
| BA9s bayonet (T4W, 233) | Small bulb with a round metal cap and two side pins: push in and twist. | Older cars and some vans: interior and dashboard lights, some number plate lights. | See on Amazon |
The numbers in brackets are the common UK and European names for the same bulb. The festoon numbers (239, 272, 264) are sold in slightly different lengths depending on the maker, so length matters more than the number.
How to check yours in five minutes
- Look up the bulb table in the handbook (often under "Changing bulbs" or "Technical data"). If a light is not in the table, it is a sealed LED unit.
- Prise off the lens with a plastic trim tool, starting at the notch if there is one.
- Read the type on the glass or base (W5W, C5W, T4W, or a length such as 36 mm).
- For a festoon, measure tip to tip in millimetres and buy that length.
- On a car that monitors bulbs, choose CANbus or error-free LEDs, at least for the number plate lights.
LEDs and dashboard errors
An LED draws much less current than a filament bulb. Cars that monitor their lights can read that as a blown bulb, then show a warning or make the LED flicker. Interior circuits are rarely monitored, number plate lights more often. The full explanation is in LED interior bulbs and CANbus errors, explained.
Bulbs we would start with
- Osram Night Breaker LED W5W (pair): W5W/T10 LED pair; road use only on vehicles in Osram's approval list, fine for interior lights.
- Philips Ultinon Pro6000 W5W LED (6000K): Cool white W5W; road-legal only as a position light on listed models.
- Philips Ultinon Pro6000 W5W LED (4000K warm white): Warmer white for map and dome lights.
- AUXITO T10 W5W LED Bulbs (10 pack): Cheap multi-pack to swap every small interior bulb at once.
- XELORD 39 mm Festoon LED Bulbs (pair): For dome lights that use a festoon bulb rather than W5W.
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Frequently asked questions
How do I find out which interior bulbs my car takes?
Prise off the light lens (a plastic trim tool avoids scratches) and look at the bulb: a push-in glass base is a W5W, a tube with pointed caps at both ends is a festoon, a round metal cap with side pins is a BA9s. The type and wattage are usually printed on the glass or the base. The handbook's bulb table lists them too.
How do I measure a festoon bulb?
Measure the old bulb from tip to tip in millimetres. Festoons in the same family (for example 239 and 272) are sold in slightly different lengths, so buy the length you measured; a bulb that is too short falls out of the clips and one that is too long will not fit.
Will LED interior bulbs cause a dashboard warning?
Interior lights are rarely monitored, so warnings are uncommon. Cars that check bulbs (often VW group, BMW, Mercedes and some Ford models) can flicker an LED or report a fault, mostly on number plate lights. Buy CANbus or error-free LEDs for monitored circuits.
Can I fit any colour in the number plate light?
No. The Road Vehicles Lighting Regulations require the rear registration plate lamp to be white. A blue or coloured number plate LED can fail the MOT. Inside the car, colour is up to you, as long as it does not dazzle you at night.
My car has no bulb in the dome light. Why?
Many recent cars use LED light units fixed to a circuit board. There is no bulb to change: if one fails, the whole unit is replaced. Check the handbook's bulb table before buying: if the light is not listed, it is a sealed LED unit.
Sources: Road Vehicles Lighting Regulations 1989, Schedule 15 (rear registration plate lamp: white); UK bulb retailers' festoon listings for lengths (autobulbsdirect.co.uk);Ring bulb application guide for bulb names.