H4 and H7 bulbs are the two most common halogen headlamp bulbs fitted to tractors, telehandlers, and farm vehicles in the UK. The H4 bulb is a dual-filament unit that provides both dipped and main beam from a single bulb. The H7 bulb is a single-filament unit that handles one beam function only. The two bulbs use different bases and they are not interchangeable.
This guide explains each bulb in detail, sets out the wattage and output ranges, answers the swap question directly, and lists the agricultural vehicles each bulb fits.
H4 vs H7 at a Glance
The fastest way to tell H4 and H7 apart is by counting filaments and checking the base. H4 bulbs have two filaments and a flat three-tab base coded P43t. H7 bulbs have one filament and a two-tab base coded PX26d.
| Specification | H4 | H7 |
|---|---|---|
| Filaments | 2 | 1 |
| Base code | P43t | PX26d |
| Beam function | Dipped and main beam | Single beam (dipped or main) |
| Common 12V wattage | 60/55W | 55W |
| Common 24V wattage | 75/70W | 70W |
| Connector pins | 3 | 2 |
| Interchangeable | No | No |
A tractor that runs a single combined headlamp on each side usually takes H4. A tractor or telehandler that runs separate headlamps for dipped and main beam usually takes two H7 bulbs per side, one for each function.
What Is an H4 Bulb
An H4 bulb is a dual-filament halogen bulb designed for headlamps that produce both dipped and main beam from a single unit. The standard H4 base is the P43t, which uses three flat metal tabs to lock into the headlamp socket and a three-pin electrical connector to power the two filaments and the shared earth.
H4 bulbs are widely used on older European cars, motorcycles, vans, and a large share of the UK agricultural fleet. Tractors built between the 1980s and the late 2010s often run H4 in the main forward headlamps because a single bulb halves the parts count and simplifies the wiring loom.
The two filaments inside an H4 bulb operate independently. One filament sits behind a small metal shield and produces dipped beam by directing light upward against the reflector. The other filament sits at the focal point and produces main beam by sending light directly forward. Switching between dipped and main beam energises one filament or the other.
What Is an H7 Bulb
An H7 bulb is a single-filament halogen bulb designed to produce one beam function per bulb. The H7 base is the PX26d, which uses two flat metal tabs and a two-pin connector. Each H7 bulb powers either dipped beam or main beam, never both.
H7 bulbs entered widespread use from the late 1990s and now feature in most modern cars and many newer agricultural vehicles. Manufacturers favour H7 in projector-style headlamps because a single filament gives a sharper, more controllable beam than a dual filament unit.
A vehicle that uses H7 will normally fit two H7 bulbs per side. One bulb handles dipped beam and the other handles main beam. The reflector and lens design in front of each bulb shapes the beam to UK road regulations.
Filament and Beam Function Differences
H4 produces two beams from one bulb, H7 produces one beam from one bulb. This single fact drives every other difference between the two.
The H4 design dates from the era when reflector technology was simpler and packaging space inside the headlamp was tighter. Combining both beams in one bulb saved housing space, simplified wiring, and reduced manufacturing cost. The trade-off is that the dipped beam filament sits off-centre, which produces a slightly less precise beam pattern than a single-filament alternative.
The H7 design was introduced to take advantage of more sophisticated reflector and projector optics. With one filament at a fixed focal point, the optics can be tuned tightly to produce a sharp dipped beam cut-off and a long main beam throw. The trade-off is that two bulbs are needed per side, which increases part count and wiring complexity.
For agricultural use, both bulb types perform well in their intended fitments. The H4 bulb suits older tractor headlamp housings with single-bulb optics. The H7 bulb suits newer tractors and telehandlers with separate dipped and main beam reflectors.
Wattage, Voltage, and Output
H4 and H7 bulbs are sold in 12V and 24V variants and in several wattage levels. Most agricultural vehicles run at 12V, although some larger machines and HGVs run at 24V.
| Bulb | System | Standard wattage | Output (lumens, approx) |
|---|---|---|---|
| H4 | 12V | 60W main / 55W dipped | 1,650 / 1,000 |
| H4 | 24V | 75W main / 70W dipped | 1,900 / 1,200 |
| H7 | 12V | 55W | 1,500 |
| H7 | 24V | 70W | 1,750 |
Higher-output halogen variants exist for both H4 and H7, with claims of up to 130 percent more light than standard. These variants do not increase wattage, they use a brighter gas mix and a thinner filament. Higher-output halogens are road legal in the UK provided they carry the correct E-Mark approval.
Voltage matters. Fitting a 12V H4 to a 24V tractor will blow the bulb on the first switch-on. Fitting a 24V H4 to a 12V tractor will produce a dim, orange light because the filament is not getting its rated power. Always match the bulb voltage to the tractor electrical system. For more on this, see 12V vs 24V Lighting Systems.
Are H4 and H7 Interchangeable
H4 and H7 bulbs are not interchangeable. The bases are different, the connectors are different, and the headlamp optics are designed around one bulb type or the other.
The P43t base on an H4 bulb will not fit into a PX26d socket on an H7 housing. The locking tabs are positioned differently, the flange diameter is different, and the connector pin spacing is different. Forcing one bulb into the wrong socket damages the housing and creates a fire risk.
Even with adapter rings or wiring modifications, swapping H4 for H7 (or the other way) defeats the headlamp optics. The reflector behind an H4 bulb is shaped to handle a dual-filament source. Putting a single H7 filament in that space produces a beam pattern that scatters light upward, dazzles oncoming drivers, and fails an MOT or DVSA roadside check.
The correct rule is simple. Fit the bulb the manufacturer specifies. Check the headlamp body, the owner’s manual, or a parts catalogue before ordering. If the headlamp has a three-pin connector and a flat triangular base, it takes H4. If the headlamp has a two-pin connector and a smaller flange, it takes H7.
Which Tractors and Farm Vehicles Use H4 and Which Use H7
H4 fitment dominates older tractors and many compact and utility models. H7 fitment dominates newer, larger tractors, telehandlers, and machines with projector-style headlamps. The dividing line is not absolute, but the table below shows the common pattern.
| Manufacturer | Common H4 fitment | Common H7 fitment |
|---|---|---|
| John Deere | 5R, 6010 to 6030 series cabs | Newer 6R, 7R, 8R series |
| New Holland | T5, T6, TS series | T7 LWB, T8 |
| Massey Ferguson | 5400, 6400, older 6700 | 7700S, 8700S, newer 6S |
| Case IH | Maxxum pre-2015, JX | Puma, Magnum, Optum |
| Fendt | 200 Vario older | 700, 800, 900 Vario |
| JCB | Older Loadall 526 to 535 | Newer Loadall 536 to 542, Fastrac |
| Kubota | M-series compact | M7, larger utility models |
Always confirm the fitment on the specific machine. The correct way to check is to remove the existing bulb, read the part code stamped on the glass envelope, and order a replacement that matches. The Tractor Light Fitment Guide explains how to identify any tractor lighting part by VIN, model, and year.
LED Conversions for H4 and H7 Sockets
LED replacement bulbs are available in both H4 and H7 fittings, and they retrofit directly into the existing socket without modifying the headlamp body. An LED H4 bulb has two LED arrays inside one housing to replicate the dipped and main beam functions. An LED H7 bulb has one LED array.
LED retrofits offer three measurable advantages over halogen. Light output rises to between 4,000 and 6,500 lumens per bulb, well above halogen levels. Power draw drops to around 18 to 30 watts per bulb. Lifespan extends to 30,000 hours or more, against 500 to 1,000 hours for halogen.
The trade-offs are also clear. Most LED retrofit bulbs are not E-Mark approved for use in UK headlamps on the road, even though they fit the socket. The DVSA position is that retrofitting a non-approved LED into a headlamp originally type-approved for halogen makes the headlamp non-compliant. For off-road, yard, and farm-track use, this is a low risk. For road-legal use, the only fully compliant route is a complete LED headlamp unit with its own E-Mark approval.
The full picture is covered in LED Headlamp Conversions: How to Upgrade from Halogen to LED, which sets out the legal position and the practical fitting steps.
How to Replace an H4 or H7 Bulb
The replacement procedure is similar for both bulb types and most tractor headlamps follow the same access pattern.
- Disconnect the battery isolator before working on any vehicle electrics.
- Open the bonnet or remove the bonnet panel covering the headlamp.
- Locate the rear of the headlamp housing and pull off the rubber dust boot.
- Unclip the wire retaining spring (H4 and H7) or rotate the locking ring (some H7 fitments) anti-clockwise.
- Pull the old bulb straight out of the socket without touching the glass envelope.
- Take the new bulb out of its packaging holding only the metal base.
- Align the locating tabs with the slots in the headlamp socket and push the bulb home.
- Refit the retaining spring or locking ring.
- Refit the dust boot, ensuring it seats fully against the housing.
- Reconnect the battery and test both dipped and main beam.
The single most common cause of premature halogen failure is finger contact on the glass envelope. Skin oils create hot spots on the bulb when it heats up, and those hot spots crack the glass. If the glass is touched accidentally, wipe it with isopropyl alcohol on a clean cloth before fitting.
Common Faults with H4 and H7 Bulbs
H4 and H7 bulbs share most of the same failure modes. The pattern of failure usually points to the underlying cause.
A blackened envelope on a working bulb indicates the bulb is approaching end of life. Replace it before the filament breaks. A blackened envelope on a failed bulb confirms normal wear-out at the end of its rated 500 to 1,000 hours.
A cracked envelope or a melted base indicates overheating, which usually traces back to a damaged dust boot allowing water ingress, or finger contact on the glass during fitting.
A bulb that lasts under 50 hours indicates a charging-system fault. The alternator is overcharging, pushing 14.8 volts or more into a 12V system, which forces the filament beyond its design temperature. Test the charging system before fitting another bulb.
A bulb that flickers indicates a poor earth or a corroded connector pin. Clean the connector terminals with contact cleaner and check the earth bond from the headlamp housing to the chassis.
For a full diagnostic process across all tractor lighting faults, see How to Troubleshoot Tractor Lighting Problems.
H4 and H7 are not interchangeable, they fit different sockets, and each has a clear set of agricultural fitments. Always confirm the bulb type on the specific machine before ordering. For replacement halogens, LED retrofit options, and full headlamp assemblies, the Universal Headlamps category covers H4, H7, and the full halogen and LED range.