H4 Bulbs Explained: Fitting, Wattage and Which Cars Use Them

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H4 is the single most common headlight bulb fitting on UK roads, and it is also the one people most often get wrong. This guide covers what an H4 actually is, why it will never swap for an H7, how to tell which one your car takes, and — the bit almost every other page ducks — exactly where aftermarket LED “upgrade” bulbs stand with the MOT.

What an H4 bulb actually is

H4 is a filament light source category defined under UN Regulation 37, the international standard that governs headlight bulbs. That standard is where the real specification lives, and it is worth starting there because most retailer pages skip it entirely.

Two details worth knowing. First, the cap designation in UN R37 is P43t — you will see some retailer copy write it as “P43t-38”, and that suffix does not appear in the regulation. Second, you will often see “H4 = 9003” or “H4 = HB2”. Those are US trade cross-references, not ECE categories; HB2 does not appear in the UN R37 category list at all. If you’re buying in the UK, look for H4 or 472.

Why an H4 will never fit an H7 socket

There are three separate reasons, and each one on its own would be enough.

1. The base is physically different. P43t and PX26d are different cap designs. As HELLA — a headlamp manufacturer — puts it, an H4 lamp does not fit an H7 socket and vice versa.
2. The filament count is different. An H4 has two filaments and produces both dipped and main beam from one bulb. An H7 has one, so a car using H7 needs two bulbs per headlamp to do both jobs.
3. The reflector is matched to the filament position. The reflector inside your headlamp is designed around exactly where the filament sits. Change the light source and the beam is projected incorrectly onto the road — which is a safety problem for you and for oncoming drivers, not just a performance one.

HELLA’s own summary is blunt: it is not possible simply to replace H4 lamps with H7 lamps. Our H4 vs H7 comparison covers the differences in more depth.

Single-bulb and separate-bulb headlight systems

This is the bit that resolves most of the confusion, and it explains why some cars need two bulbs and others need four.

A single-bulb H4 system uses one P43t bulb per headlamp, doing both jobs. The dipped filament has a small shield below it that cuts off the upward light; the main filament sits at the reflector’s focus. Two bulbs per car. Cheaper to replace, but both beams fail together when a bulb goes.

A separate-bulb system uses one single-filament bulb per function per side — four bulbs in total. H7 is the most common dipped-beam bulb in this arrangement, paired with a different single-filament type for main beam. HELLA notes that separate systems generally achieve higher luminous efficiency because of the combined effect of two lamps, at the cost of twice as many bulbs to replace.

The other headlight bulb categories you will meet

All of the following are genuine UN R37 filament categories.

Two important exclusions from that list, because they are frequently lumped in with it:

• D1S, D2S, D3S and D4S are not R37 categories. They are gas-discharge (xenon/HID) light sources governed by UN Regulation 99, running at roughly 85V and 35W with entirely different caps — D2S uses a P32d-2 cap. They are physically and electrically unrelated to a 12V halogen bulb.
• LED light sources sit under UN Regulation 128, where approval attaches to the complete lamp unit rather than to a bulb. That distinction is exactly why there is no approval route for a drop-in LED replacement — see the legal section below.

Our car bulb types explained guide covers the full range.

Which cars take H4

H4 is still very widely used in the UK — you will find it on superminis and older hatchbacks, on vans, and on the base halogen trims of cars that offered xenon or LED headlights further up the range. But “common” is not the same as “yours”, and the model name on its own will not settle it.

The reliable route is to check your specific car rather than work from a generic list. Our car parts compatibility checker covers bulb fitments across 68 UK models, and each model has its own bulb page listing the dipped, main and ancillary fittings. Confirm that against the marking on the bulb you actually remove before ordering.

Why the answer changes within the same model

This is the single biggest cause of buying the wrong bulb, and almost no other page addresses it.

A car offered with factory xenon does not use a halogen bulb at all — it uses a gas-discharge source under UN R99, at about 85V, with a completely different cap. So two cars that are the same model, the same year and the same colour can take entirely different light sources depending on which options box was ticked when they were built. Facelifts change it too, as do market-specific specifications.

Narrow it down with our car parts compatibility checker, then confirm physically before you order.

What “+150%” and “+220%” actually mean

Performance halogen bulbs are sold on brightness claims, and those claims are real — but they are not measured against the bulb you are taking out.

OSRAM and Philips both state their baseline clearly, and it is the legal minimum. OSRAM’s footnote reads “compared to minimum ECE R112 requirements”. Philips states “brightness compared to legal minimum standard”. So a “+220%” bulb is 220% brighter than the dimmest bulb the regulations would permit — not 220% brighter than the perfectly good bulb currently in your car.

Ring and Bosch are vaguer. Ring says “more light on the road ahead” and, for its 150 product, “80m longer beam pattern than standard halogens”. Bosch says “compared with standard halogen bulbs”. Neither cites the ECE minimum as the reference point.

The trade-off nobody advertises

No manufacturer prints a sentence saying “this bulb will not last as long”. But OSRAM publishes the service-life figures for its own products, and the gap is substantial.

By OSRAM’s own numbers, the high-performance bulb has roughly a third of the standard bulb’s B3 life on the first filament, and about a tenth of the long-life bulb’s on the second. That is not a reason to avoid them — a brighter dipped beam is worth something — but it is worth knowing before you fit a pair and expect them to last as long as the ones that came out.

Which H4 bulb to buy

All the products below are ECE-approved halogen bulbs and are legal replacements for an H4 halogen headlamp in the UK. We do not list LED or HID retrofit bulbs here — see the legal section below for why. Product lines and part numbers verified against manufacturers’ own catalogues, August 2026.

Maximum brightness

OSRAM NIGHT BREAKER 220 — part number 64193NB220. OSRAM’s current top halogen line, claiming up to 220% more brightness against the minimum ECE requirement. Note the supersession: NIGHT BREAKER 200 is no longer the current generation. Expect a shorter service life than a standard bulb.
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Philips RacingVision GT200 — part number 12342RGTS2. Up to 200% brighter than the legal minimum standard, with a stated beam reaching over 80 metres further. Philips gives a 400-hour lifetime for this product.
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Ring Xenon220 — part number RX2272. Ring’s current performance H4. Note that the previous Xenon200 (RX2072) was discontinued in May 2026 and superseded by this one, so ignore older recommendations pointing at RX2072.
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A balance of brightness and life

Philips X-tremeVision Pro150 — part number 12342XVPS2. Up to 150% brighter than the legal minimum, with a longer stated life than the GT200.
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OSRAM NIGHT BREAKER LASER — part number 64193NL. Up to 150% brighter than the minimum legal standard.
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Longest life — the sensible choice for awkward headlights

OSRAM ULTRA LIFE — part number 64193ULT. Up to four times the lifetime of a standard halogen bulb, up to 100,000 km, with a four-year OSRAM guarantee. Worth it on any car where changing a headlight bulb means removing the bumper or the wheel arch liner.
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Philips LongLife EcoVision — part number 12342LLECOB1 (single) or 12342LLECOS2 (twin pack). Sold on longevity: Philips states drivers should not have to change a headlamp for at least 100,000 km.
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Standard replacement

OSRAM ORIGINAL LINE — part number 64193. OE-quality standard H4. 250-hour B3 life on the first filament, considerably more than the performance bulbs.
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Ring standard H4 — part number R472. ECE R37 approved, road legal, OE quality.
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LED “upgrade” bulbs: the UK position

We do not sell bulbs, so we can be straightforward about this where retailers who stock LED retrofits usually hedge.

Fitting an LED bulb into a headlamp designed for a halogen bulb is an MOT failure. The DVSA MOT inspection manual, section 4.1.4, states that existing halogen headlamp units on vehicles first used on or after 1 April 1986 must not be converted to use HID or LED bulbs. The relevant defect is recorded as “light source and lamp not compatible”, and it is categorised as a Major defect — which means a fail.

Separately from the MOT, the Road Vehicles Lighting Regulations 1989 require an approval mark or a British Standard mark on dipped-beam headlamps for vehicles first used on or after the same date, 1 April 1986. The two thresholds line up. An LED bulb dropped into a reflector approved for a filament source cannot carry a valid approval for that combination, because approval attaches to the lamp unit together with its designated light source category.

Three things worth being precise about

• Factory LED and factory xenon headlamps are a different case entirely. Complete headlamp units manufactured with LED or HID sources are not caught by this — though they do carry extra requirements at MOT, including working self-levelling and headlamp washers, where a malfunction is a Major defect.
• “Off-road use only” is a retailer disclaimer, not a legal permission. Nothing in the lighting regulations creates an off-road category for headlamp light sources. A bulb sold with that wording is being sold with a caveat, not an exemption.
• Passing an MOT does not make a conversion legal. The test does not permit dismantling, so it is possible for a non-compliant conversion to go unnoticed on the day. That is not the same as it being roadworthy.

Full detail in our guide to LED headlight bulbs and UK law, and what else the test covers in our car bulbs MOT guide.

How to work out which bulb your car takes

1. The handbook first. It is the most authoritative source for your specific build.
2. A registration lookup to shortlist. Fast, but database coverage has gaps, particularly on newer models.
3. Read the marking on the bulb you remove. This is the only method that tells you what is physically fitted right now, and it is the one to rely on if the car is a facelift-year example or was offered with factory xenon.
4. Ask the manufacturer if the first three leave you unsure.

Frequently asked questions

Can I put an H7 bulb in an H4 socket?

No. The caps are different (P43t versus PX26d), the filament counts are different, and the reflector is designed around the filament position. It will not physically fit, and it would not produce a correct beam pattern if it did.

Is an H4 the same as a 472?

Yes. 472 is the UK trade number for an H4 bulb. Some packaging shows one, some shows both.

What is the difference between H4 and 9003?

9003 is a US trade cross-reference for the same physical bulb. Note that HB2, which is sometimes quoted alongside it, does not appear in the UN R37 category list — in the UK, buy on H4 or 472.

Will LED H4 bulbs fail the MOT?

Yes, on any vehicle first used on or after 1 April 1986. The DVSA manual records it as “light source and lamp not compatible”, a Major defect.

What wattage is an H4 bulb?

60/55W at 12V — 60W on main beam, 55W on dipped. At 24V the rating is 75/70W.

Do I need to replace both headlight bulbs at the same time?

Not a requirement, but a sensible habit. Bulbs fitted at the same time age at similar rates, and a mismatched pair of headlamps differing in colour is itself a Major MOT defect.

Why does my car use two different bulb types for dipped and main beam?

Because it uses a separate-bulb system rather than a single H4. Each function has its own single-filament bulb, so the car needs four bulbs rather than two.

Are “+220%” bulbs really more than twice as bright?

Compared to the dimmest bulb the regulations allow, yes — that is the baseline OSRAM and Philips state. Compared to the working bulb you are replacing, the difference is smaller. Expect a shorter service life too.

Related guides

• H4 vs H7 headlight bulbs
• Car bulb types explained
• Are LED headlight bulbs legal in the UK?
• Car bulbs and the MOT
• How to change a headlight bulb

How we check fitment for this guide

The bulb specifications on this page come from UN Regulation 37 itself, cross-checked against manufacturers’ published catalogues, rather than from retailer listings. The MOT and lighting-regulation positions are taken from the DVSA MOT inspection manual and the Road Vehicles Lighting Regulations 1989 directly.

Which bulb a specific car takes depends on model year, facelift, trim and factory options — a car specified with factory xenon uses a different type of light source altogether. Narrow the choice with a registration lookup, confirm against your handbook, and check the marking on the bulb you remove before ordering. How we check fitment.

Last verified: August 2026. We review this page every six months, as DVSA guidance on headlamp conversions changes.