A halogen headlamp bulb is a tungsten-filament lamp pressurised with halogen gas, designed to deliver bright forward light from a 12V or 24V vehicle electrical system. The four most common halogen headlamp bulbs on UK tractors, combines and farm vehicles are H1, H3, H4 and H7. Each code defines a fixed filament position, a specific base shape, and a rated wattage that the headlamp reflector is built around. Fitting the wrong code damages the lens, ruins the beam pattern, and in some cases breaks the bulb on first start.
This guide explains what each H-code means, where each bulb fits, and how to find the right halogen replacement for a working agricultural vehicle. Specifications come from ECE Regulation 37, the international standard that governs filament lamps for road use.
How the H-Code Bulb System Works
The H-code is a fitment standard defined by ECE Regulation 37 (United Nations Economic Commission for Europe). Each code locks down three things: the base geometry, the filament position relative to the base, and the rated wattage at the rated voltage. A reflector designed for an H4 collects light from one specific filament location; a different bulb code with the same wattage will not produce the right beam, even if the bulb physically fits.
The “H” stands for halogen, the filament gas that allows the bulb to run hotter and brighter than a vacuum-filled incandescent. Numbers (1, 3, 4, 7, 11, 13, 15, etc.) identify each separate filament arrangement. Older codes (H1 to H4) date back to the 1960s and 1970s. Newer codes (H7 onwards) followed reflector and projector design changes from the 1990s.
UK agricultural vehicles use H1, H3, H4 and H7 most often. H4 dominates older British and European tractors built before 2010. H7 appears on newer machines and on dual-headlamp setups where one bulb handles dipped beam and a second handles main beam separately. H1 and H3 turn up in auxiliary, fog, spot and work-light housings as well as in some main headlamps.
Two industry trade codes also describe the same bulbs in UK parts catalogues: H4 is sold as 472 and H7 is sold as 499. The codes are identical to the ECE standard; only the catalogue number differs.
H1 Bulbs: Single Filament, P14.5s Base
H1 bulbs are single-filament halogen lamps with a P14.5s base, rated 55W at 12V and 70W at 24V. The single filament sits at the geometric centre of the reflector and the base clips into a sprung wire retainer. H1 is the workhorse of separate-housing main beam and auxiliary lamps.
A typical H1 bulb produces 1,550 lumens at 12V 55W, with a colour temperature of 3,200K. Lifespan is 400 to 1,000 hours under road use. Standard automotive brands (Osram, Philips, Hella, Narva) all carry H1 in clear, blue-tint and high-output forms.
H1 fits where the headlamp design uses one bulb per function. On a four-headlamp tractor or 4×4, the inner pair often hold H1 main beams. The outer pair may hold a different code such as H4 or H7 for dipped beam. H1 also fits many original-equipment fog lamps, driving lamps and spot lamps from Hella and Wipac.
For stock numbering, H1 is often listed as 448 in UK trade catalogues. The base shape is sometimes called “single-pin” because of the single male spade terminal protruding from the base.
H3 Bulbs: Fog and Spot Lamp Bulb
H3 bulbs are single-filament halogen lamps with a PK22s base and a flying lead wire instead of a fixed terminal. Wattage is 55W at 12V (35W variants exist for low-output applications). The PK22s base seats in a circular socket and a single retaining clip holds it in place.
H3 fits fog lamps, spot lamps, auxiliary driving lamps and rear work lamps where a wide pencil beam is wanted. The bulb is shorter than H1 and H4, which lets it fit deeper inside a fog reflector without the lead-wire fouling on the rear cover.
A typical H3 produces 1,450 lumens at 12V 55W, with a colour temperature of 3,200K. Lifespan is 400 to 1,000 hours. Most UK agricultural fog lamps and many older tractor work lamps from Hella, Britax, and Sim use H3.
H3 industry trade code in UK catalogues is 453. Replacement bulbs are widely stocked because H3 also appears in large numbers of cars, vans and motorcycles.
H4 Bulbs: Dual Filament, Industry Code 472
H4 bulbs are dual-filament halogen lamps with a P43t base, used wherever a single headlamp delivers both dipped beam and main beam. Wattage is 60W main and 55W dipped at 12V (75W/70W at 24V). The base has three flat blade terminals and a keyed flange that locks the bulb at one rotational position.
The two filaments inside an H4 sit at different heights inside the bulb. The dipped-beam filament sits behind a small metal cap that blocks light from the lower half of the reflector, producing the asymmetric cut-off pattern required by ECE law for European right-hand-drive traffic. The main-beam filament sits below the cap and uses the full reflector.
A typical H4 bulb produces 1,650 lumens on main beam and 1,000 lumens on dipped beam at 12V. Colour temperature is 3,200K. Lifespan is 450 to 1,000 hours.
H4 fits the largest share of UK agricultural headlamps built between 1980 and 2010, including most John Deere 6000-series tractors, New Holland TS and TM ranges, Massey Ferguson 4200 to 6500 series, Case IH MX and JX series, and a long list of older models. The industry trade code is 472.
H4 has held its position because it does the job of two bulbs (dip and main) in one fitting, simplifying the headlamp body and saving cost. Modern reflector and LED designs are now displacing it on new machines, but the installed fleet of H4-fitted tractors in the UK still runs into the hundreds of thousands.
H7 Bulbs: Single Filament, Industry Code 499
H7 bulbs are single-filament halogen lamps with a PX26d base, rated 55W at 12V and 70W at 24V. The PX26d base has a flat retaining flange with two small lugs, two terminal blades, and a key tab that locates the bulb at one rotational position.
H7 is the standard “one bulb, one function” replacement for H1 in newer headlamp bodies. A complete H7 headlamp uses two bulbs per side: one for dipped beam, one for main beam. This split lets each filament sit in its own dedicated reflector or projector, producing a cleaner cut-off than the dual-filament H4 design.
A typical H7 bulb produces 1,500 lumens at 12V 55W with a colour temperature of 3,200K. Lifespan is 400 to 800 hours under road duty. Modern higher-output H7 bulbs (Osram Night Breaker, Philips RacingVision) push lumen output to 1,950 with the same wattage, at the cost of shorter life (200 to 300 hours).
H7 fits newer tractors and combines built from the late 1990s onwards, including most Fendt 700-series, John Deere 7R and 8R, New Holland T7 and T8, and Claas Lexion combines. The industry trade code is 499.
H1, H3, H4, H7 Side by Side
The four bulbs differ in base, filament count, wattage and fitment. The table below covers the four most common variants in UK 12V agricultural fitments.
| Code | Base | Filaments | Wattage 12V | Lumens (typical) | Industry code | Common use |
|---|---|---|---|---|---|---|
| H1 | P14.5s | 1 | 55W | 1,550 lm | 448 | Main beam, spot, fog |
| H3 | PK22s | 1 | 55W | 1,450 lm | 453 | Fog lamp, spot, work lamp |
| H4 | P43t | 2 (main + dip) | 60/55W | 1,650 / 1,000 lm | 472 | Combined dip/main headlamp |
| H7 | PX26d | 1 | 55W | 1,500 lm | 499 | Dip OR main in twin-bulb headlamp |
Voltage variants matter on ag equipment. A 24V tractor takes 70W versions of H1 and H7, and 75/70W versions of H4. Fitting a 12V bulb in a 24V system burns the bulb out in seconds. Fitting a 24V bulb in a 12V system runs the lamp dimly with no protection issue, but it never produces the rated lumen output.
For a deeper look at how filament technology compares with newer LED headlamps, see LED vs halogen tractor lights.
Finding the Right Bulb for Your Tractor or Combine
Identify the bulb by reading the marking on the metal base or the glass collar of the existing lamp. ECE-approved bulbs carry the H-code printed clearly on the base, alongside the wattage (e.g., “H7 12V 55W”) and an E-mark with country and approval number (e.g., E1, E11, E13). The trade code (472, 499, 453, 448) often appears on the box but not always on the bulb itself.
Step-by-step identification:
- Pull the headlamp connector off the rear of the bulb.
- Release the retaining clip or twist the bulb holder if it has one.
- Remove the bulb without touching the glass with bare fingers (skin oils shorten halogen life).
- Read the H-code printed on the metal base or glass.
- Note the wattage (55W or 70W) and the voltage (12V or 24V).
- Match all four values when buying the replacement.
If the existing bulb is broken or the marking has rubbed off, find the model and year of the headlamp body. Most agricultural OEMs list the bulb code in the operator’s manual or on the lamp body itself. Aftermarket lamp bodies from Hella, Britax, Cobo, Carello and Sim print the bulb code on the inside of the housing or on the rim.
For tractors with sealed-beam headlamps (no separate bulb, the entire lamp is one unit), there is no H-code at all. Sealed beams are a different category covered in a separate guide. See tractor headlights for a wider fitment overview.
A small number of agricultural headlamps use less common codes such as H8, H9, H11, H15 and HB3/HB4 (9005/9006). These codes follow the same ECE R37 logic but differ in base shape and wattage. Always check before ordering.
Halogen Replacement, High-Output Halogen, or LED Conversion
Three replacement paths exist when a halogen bulb fails: stock halogen, high-output halogen, or an LED retrofit. Each path has different cost, output, lifespan and legal implications for road use.
Stock halogen replacement is the cheapest at GBP 4 to GBP 12 per bulb. Output and lifespan match original equipment. Road legal in any UK vehicle, agricultural or otherwise. Best for trailers, occasional-use machines and budget-conscious operators.
High-output halogen (Osram Night Breaker 200, Philips RacingVision GT200, Narva Range Power +150) costs GBP 18 to GBP 35 per bulb. Output rises by 150 to 200 percent at the same wattage. Lifespan drops to 200 to 400 hours. Road legal because the bulb still meets the ECE-approved wattage and pattern. A worthwhile upgrade for active operators on H4 and H7 fitments.
LED retrofit uses an LED bulb with the same H-code base. Cost is GBP 25 to GBP 90 per bulb. Output rises to 4,000 to 12,000 lumens. Lifespan is 30,000 to 50,000 hours. Power draw drops by 60 to 80 percent. Road legality is conditional. An LED retrofit in an original halogen reflector usually does not hold a valid ECE approval, which means the headlamp loses its road-legal status under UK Construction and Use Regulations.
The full LED conversion path, including which kits hold valid type approval and which do not, is covered in LED headlamp conversions.
For purchase, see the halogen and LED bulb ranges at Agri Lighting. Stock halogen bulbs in H1, H3, H4 and H7 are typically held in 55W and 70W variants for both 12V and 24V vehicles.
Halogen Headlamp Bulb Quick Reference
The H-code system makes halogen headlamp replacement a five-minute job once the right code is identified. H1 for single-filament main beam and auxiliary use. H3 for fog, spot and work lamps. H4 for combined dip and main beam in one bulb. H7 for single-filament dip or main in a twin-bulb headlamp. The base, filament count and wattage all change between codes, and a wrong substitution either fails to fit or damages the reflector. Match the H-code, the voltage and the wattage on every replacement.
For wider lighting context, see the complete guide to tractor lighting and the LED vs halogen technology comparison.