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Why Are There So Many Bulb Types?
Different bulb types exist because headlight designs vary between manufacturers. Each type has a specific base, filament position, and wattage that matches a particular headlight reflector design. Using the wrong type means the bulb physically won’t fit, or if forced in, will produce a dangerous beam pattern.
Headlight Bulbs
| Type | Base | Wattage | Common Use |
|---|---|---|---|
| H1 | P14.5s | 55W | Main beam, fog lights |
| H4 | P43t | 60/55W | Combined dipped/main beam (older cars) |
| H7 | PX26d | 55W | Dipped beam (most common since ~2000) |
| H11 | PGJ19-2 | 55W | Fog lights, some dipped beams |
| H15 | PGJ23t-1 | 55/15W | DRL + main beam (VW Group, Ford) |
| HB3 (9005) | P20d | 60W | Main beam (Japanese/Korean cars) |
| HB4 (9006) | P22d | 51W | Fog lights |
| H8 | PGJ19-1 | 35W | Fog lights |
| H9 | PGJ19-5 | 65W | Main beam |
| H16 | PGJ19-3 | 19W | Fog lights, DRL |
Recommended Bulbs
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H8, H9, H11 and H16 share the PGJ19 cap family, but they are keyed differently and run different wattages — they are not interchangeable. Fitting a 55W H11 where the lamp was approved for a 35W H8 changes the light source the lamp was type-approved with. Cap codes and wattages per UN Regulation No. 37, Annex 1. Last verified August 2026.
Signalling & Auxiliary Bulbs
| Type | Wattage | Use |
|---|---|---|
| W5W (501) | 5W | Sidelights, number plate |
| P21W (382) | 21W | Brake light, reverse light, rear fog |
| PY21W (581) | 21W | Indicator (amber coated) |
| W21W (582) | 21W | Indicator, reverse (wedge base) |
| P21/5W (380) | 21/5W | Combined tail/brake light |
| C5W (239) — 11×39mm; festoon lengths vary, so check yours | 5W | Interior, number plate (festoon) |
Gas-discharge (HID) and LED
The H-series above are all halogen filament lamps, approved under UN Regulation 37. Two other families exist and are governed separately:
- D1S, D2S, D3S, D4S and their D…R variants are gas-discharge (xenon) burners under UN R99. They run at high voltage through a ballast and are not a drop-in replacement for a halogen bulb.
- LED light sources are covered by UN R128, whose categories are LW, LY and LR designations for lamps designed around them. There is no R37, R99 or R128 category that authorises an LED replacement for an H1, H4, H7 or H11 — which is why retrofit LED bulbs fail the MOT. See our guide to LED headlight bulbs and UK law.
- On many cars from the mid-2010s onward the headlamp is a sealed LED unit with no user-replaceable bulb at all. If there is no bulb holder behind the lamp, that is usually why.
How to Find Your Bulb Type
The easiest way is to use our car bulb finder — select your make and model for a complete list of every bulb in your car. Alternatively, check your vehicle handbook or look at the markings on the existing bulb.
Frequently Asked Questions
What’s the most common headlight bulb?
H7 is very common as a dipped beam bulb on cars from the late 1990s onward, where dipped and main beam have separate bulbs and reflectors. H4 remains widespread where a single bulb does both jobs. No published dataset breaks the UK vehicle parc down by bulb type, so check your own car rather than relying on a rule of thumb.
Can I use H7 instead of H4?
No — they have completely different bases and are not interchangeable. H4 has two filaments (dipped + main beam), while H7 has one.
What do the bulb numbers mean?
The ‘H’ stands for halogen. The number indicates the specific base type and filament design. They don’t indicate brightness or quality.
Are all H7 bulbs the same quality?
No — premium H7 bulbs from Philips or OSRAM produce significantly more light than budget alternatives, while still meeting legal wattage limits.
H4 and H7 are the two fittings you will meet most often. H4 is used where a single bulb produces both dipped and main beam; H7 where dipped and main have separate bulbs and reflectors, the layout that became normal on cars from the late 1990s onward. Our H4 bulbs guide covers the full specification, why it will never swap for an H7, and exactly where LED upgrade bulbs stand with the MOT.
Recommended Products
Philips RacingVision GT200
Up to 200% more light than the legal minimum standard (Philips’ own claim)
Osram Night Breaker Laser
Up to 150% more light than the minimum ECE R112/R37 requirement (OSRAM’s own claim)
How we check fitment for this guide
We cross-reference fitment figures against manufacturer specifications and OE-supplier catalogue data where available, and matched to the standard codes that actually govern fit — battery type/group sizes, wiper lengths and fitting types, bulb fitment codes, tyre size markings, and oil specifications. We work by make, model, year, engine, and build date, because a single model can take different parts across its life. Where the right part depends on your exact vehicle, we tell you to confirm by registration or VIN. More on our method →