H4 Bulbs Explained: The 472 P43t Dipped and Main Beam Headlight Bulb, and How to Fit It
An H4 bulb is the 472: a 12V 60/55W twin-filament halogen headlight bulb on a P43t base. 24V 75/70W 475, uprated bulbs, fitting tips and UK LED rules.
In this guide
An H4 bulb is a twin-filament halogen headlight bulb that gives both dipped beam and main beam from one bulb, on a P43t base with 3 connector pins. The standard 12-volt H4 is rated 60/55W (60 watts main, 55 watts dipped) and is sold in the UK as the 472. The 24-volt version is rated 75/70W and is sold as the 475.
This guide covers what the H4 code means, the P43t base, the 12V and 24V ratings and light output, where H4 bulbs are used on tractors and road vehicles, what uprated “+%” bulbs really give you, how to fit one without touching the glass, and where LED H4 bulbs stand under UK rules.
What Is an H4 Bulb?
An H4 is a halogen filament lamp category defined in UNECE Regulation 37. It has 2 filaments inside one quartz glass capsule filled with halogen gas. One filament gives main beam and the other, which sits over a small metal shield cup, gives dipped beam. The shield blocks light that would otherwise go upwards, and that is what creates the sharp cut-off on dipped beam.
Switching from dipped to main beam simply moves the power from one filament to the other. That is why an H4 headlamp needs only one bulb per side for both beams, and why the H4 became the standard bulb for a single round or rectangular headlamp on cars, vans, motorbikes and tractors.
| Specification | H4 12V | H4 24V |
|---|---|---|
| UK number | 472 | 475 |
| Wattage (main / dipped) | 60/55W | 75/70W |
| Light output (main / dipped) | 1,650 / 1,000 lumens | 1,900 / 1,200 lumens |
| Base | P43t | P43t |
| Filaments | 2 | 2 |
| Connector pins | 3 | 3 |
The light output figures are the reference values in Regulation 37, which allows a tolerance of plus or minus 15 percent. Every approved standard H4 is built to give roughly these figures.
The P43t Base and 3-Pin Connector
The P43t is a prefocus base. The metal flange has 3 locating tabs that only fit the headlamp reflector one way, so the filaments always sit at the exact point the reflector was designed around. That position is what gives a correct beam pattern and cut-off.
The 3 flat pins on the back are main beam feed, dipped beam feed and a shared earth. On most vehicles they plug into a 3-way connector with the same layout. A wire spring clip or a retaining ring in the back of the headlamp holds the bulb against the reflector.
Some older headlamps take an R2 bulb, sometimes called a Bilux, rated 45/40W at 12V on a P45t base. It looks similar to an H4 but is a different, non-halogen category with a different base, so match the old bulb before you order.
472 and 475: The UK Numbers
- 472 is the 12V 60/55W H4, the bulb most UK brands print on the box, sometimes with a prefix such as R472.
- 475 is the 24V 75/70W H4, used on lorries, buses, plant and 24V tractors.
The 472 and 475 fit the same headlamp. Fitting a 12V bulb on a 24V machine blows it almost at once, and a 24V bulb on a 12V system gives a dim, yellow light that will not light the road properly. If you are not sure which system a machine runs, see 12V vs 24V lighting systems.
H4 Bulbs in Tractor Headlamps
H4 is one of the most common headlamp bulbs on tractors and loaders because one bulb per side covers both beams and the wiring is simple. You find it in grille and bonnet headlamps on many older and mid-range tractors, in round 7-inch and rectangular replacement headlamps, and in many aftermarket headlamp units. Newer, larger tractors more often use separate H7 or LED dipped and main beam units.
Do not assume by model. The same tractor series can change headlamp type through a production run or between markets. Take the old bulb out and read the code on the base, or check the operator’s manual. If a headlamp uses one bulb per side with a 3-pin plug, it is very likely H4. If it has 2 single-filament bulbs per side with 2-pin plugs, it is likely H7. The full comparison is in H4 vs H7 bulbs, and headlamp types and upgrades are covered in tractor headlights.
Uprated and “+%” H4 Bulbs
Uprated halogen H4 bulbs are sold with claims such as +50%, +100% or +150%. They are the same 60/55W rating and the same P43t base, so they fit any H4 headlamp and are road legal when they carry the E mark and the H4 category.
The percentage is not the total light output. It refers to the light measured at a particular point in the beam, usually the area just below the cut-off that matters for seeing down the road. Total output rises far less. For example, one major maker lists its standard 12V H4 at 1,650/1,000 lumens and its +50% version at 1,815/1,100 lumens. Uprated bulbs usually have a shorter life than standard or long-life bulbs, so they suit vehicles that do a lot of night road work.
High-wattage bulbs such as 100/55W or 130/90W are a different thing. They are sold for rallying and off-road use, carry no H4 approval, draw more current than the wiring and switch may be designed for, and can melt plastic headlamps. They are not for road use. For the longest life, look at our lifetime halogen bulbs.
How to Fit an H4 Bulb Without Touching the Glass
The quartz glass of a halogen capsule runs very hot. Grease or salt from a fingertip leaves a mark that heats unevenly and can shorten the bulb’s life or crack the capsule. Handle the new bulb by the metal flange and the plastic base only.
- Switch off the lights and ignition, and turn off the battery isolator on a tractor.
- Reach the back of the headlamp. On many tractors this means lifting the bonnet or removing a grille panel or headlamp surround.
- Pull off the 3-pin connector and remove the rubber dust cover.
- Release the wire spring clip or turn the retaining ring and lift the old bulb out.
- Check the old bulb’s code and voltage: 472 for 12V, 475 for 24V. A blackened or milky capsule suggests age or water getting in.
- Hold the new bulb by the flange, line up the 3 tabs with the slots in the reflector and seat it flat.
- Refit the clip, then the dust cover, making sure the cover seals all the way round.
- Refit the connector and test both dipped and main beam.
If you touch the glass by mistake, wipe it with a clean, lint-free cloth and isopropyl alcohol before switching on. If the beam looks wrong after fitting, check the bulb is seated flat, then check headlamp aim.
Are LED H4 Bulbs Legal in the UK?
LED bulbs with an H4 base are widely sold, but fitting one in a halogen headlamp is not road legal on vehicles that take an MOT. The DVSA MOT inspection manual for cars and light vans says existing halogen headlamp units on vehicles first used on or after 1 April 1986 must not be converted to HID or LED bulbs. If they have been, the tester must fail the headlamp as a major defect for “light source and lamp not compatible”. This does not apply to complete replacement headlamp units built with LED light sources. From 14 October 2026 (a DVSA change to the MOT inspection manual) testers must also accept ECE-approved LED replacement (LEDr) bulbs that have their approval sticker fixed to the vehicle.
Some LED headlamp bulbs have gained national approval in other European countries for listed vehicles, and in 2025 the first LED replacement bulbs approved under Regulation 37 appeared, in the H11 category. The MOT now accepts approved LEDr bulbs with their sticker, but at the time of writing there is no Regulation 37 approved LED H4, so an LED H4 in a halogen headlamp still fails. Treat any “road legal” claim on an LED H4 with caution.
Most tractors are exempt from the MOT, but the lighting regulations still apply on the road. An LED bulb in a reflector designed for a halogen filament can scatter light above the cut-off and dazzle oncoming drivers. For off-road and yard use the risk is lower. For road use, the compliant way to go LED is a complete E-marked LED headlamp. Browse LED tractor headlights, or shop standard halogen bulbs for 472 and 475 replacements.
Frequently asked questions
Is a 472 bulb the same as an H4?
Yes. H4 is the ECE category and 472 is the UK trade number for the 12V 60/55W version. The 24V 75/70W H4 is the 475.
What does 60/55W mean on an H4 bulb?
The H4 has 2 filaments. The main beam filament is rated 60 watts and the dipped beam filament 55 watts. Only one works at a time.
Can I fit an H7 instead of an H4?
No. The H7 has one filament, a PX26d base and a 2-pin connector. It does not fit an H4 headlamp and cannot give both beams. See H7 bulbs explained.
Are +100% H4 bulbs legal?
Yes, if they are marked H4 with an E mark and rated 60/55W at 12V. The figure refers to light at a point in the beam rather than total output. High-wattage bulbs such as 100/55W are not road legal.
Can I put an LED H4 bulb in my tractor headlight?
It will fit, but it is not an approved combination for road use and can dazzle other drivers. For road use, fit a complete E-marked LED headlamp. For off-road work it carries less risk, but check the beam does not light up cab mirrors or other operators.