A sealed beam headlight is a single-piece headlamp where the filament, reflector and lens are sealed inside one glass unit at the factory, and the whole assembly is replaced as a single item when the filament fails. Sealed beams sit on every classic tractor built between 1940 and 1990, and many heritage models from John Deere, Massey Ferguson, Ford, International Harvester and David Brown still run them today. This guide covers the standard sealed beam sizes, the UK legal position on replacements, and the LED conversion options that fit existing housings.
What a Sealed Beam Headlight Is
A sealed beam headlight is a one-piece headlamp built as a single glass-and-steel assembly. The filament sits inside the lens. The reflector is the back surface of the glass body. The lens is the front surface, moulded with light-shaping prisms. The assembly is sealed at the factory with no removable bulb and no removable lens.
The sealed beam was invented by GE, Westinghouse and other US lamp makers in 1939, became standard on US cars and trucks from 1940, and dominated North American vehicle headlights until the early 1980s. In the UK the sealed beam appeared on imported American tractors, on commercial vehicles, and on some British tractors through the 1960s and 1970s before composite headlamps with replaceable H4 bulbs took over.
A sealed beam differs from a modern headlamp in three ways. The first is the failure mode: when the filament breaks, the whole lamp is scrap, because nothing inside it can be opened or repaired. The second is the wiring connection: sealed beams use a three-prong connector built into the back of the glass, not a separate bulb socket. The third is the beam pattern: the lens prisms create the dipped and main beam pattern, with no separate reflector adjustment available.
Standard Sealed Beam Sizes
Sealed beams come in four common sizes, with two round and two rectangular options.
| Size | Shape | Common use | Connector |
|---|---|---|---|
| 7 inch (178 mm) | Round | Single-headlamp tractors, classic cars, motorcycles | 3-prong |
| 5 3/4 inch (146 mm) | Round | Twin-headlamp tractors, US cars, light trucks | 3-prong |
| 4 x 6 inch (100 x 165 mm) | Rectangular | 1970s and 1980s US cars and trucks | 2 or 3-prong |
| 5 x 7 inch (142 x 200 mm) | Rectangular | 1980s US trucks, some tractors | 3-prong |
The 7 inch round is the dominant agricultural size. Tractors from John Deere (4020, 4430, 4640, 4840), Massey Ferguson (1100 series, 1150, 1155), International Harvester (66 and 86 series), Ford (8N, 9N, NAA, 600 series, 4000, 5000, 6610), David Brown (770, 880, 990, 1212, 1394) and many others fit 7 inch round sealed beams.
The 5 3/4 inch round appears on tractors with quad-headlamp pods or on some larger classic models. The rectangular sizes appear on US-built tractors from the late 1970s onwards and on some 1980s European machines that adopted the US standard.
A sealed beam carries a Type number on the lens that identifies its function. Type 1 is a single-filament main beam unit. Type 2 is a dual-filament unit with both dipped and main beam. A twin-headlamp tractor with four lamps typically runs two Type 2 outer lamps (dipped plus main) and two Type 1 inner lamps (main only).
How to Identify Your Tractor’s Sealed Beam
Identifying the sealed beam on a tractor takes three steps: measure the lens, check the lens markings, and inspect the connector.
Measure the lens across its widest point. A 178 mm measurement confirms a 7 inch round. A 146 mm measurement confirms a 5 3/4 inch round. A rectangle around 100 x 165 mm is a 4 x 6, and around 142 x 200 mm is a 5 x 7.
Check the lens markings. A sealed beam carries moulded markings on the lens face showing the manufacturer (GE, Westinghouse, Sylvania, Lucas, Wagner, Hella), the Type number (1 or 2), the voltage (6V, 12V or 24V) and often a wattage figure.
Inspect the connector on the back of the lamp. A standard sealed beam shows three flat prongs in a triangle pattern at the rear, sized to fit a US-pattern three-blade connector. Two-prong rectangular units use a smaller, in-line connector.
A tractor that runs sealed beams almost always has a circular or square chrome bezel around the lens, with three screws holding the lamp in place against a metal retaining ring. Newer tractors with composite headlamps show a moulded plastic housing with no visible bezel.
UK Legal Position on Sealed Beams and LED Replacements
Sealed beam headlights remain road-legal in the UK on vehicles originally built with them. The Road Vehicles Lighting Regulations 1989 accept sealed beam headlamps as a valid headlight type on vehicles registered or first used before April 1986, with no requirement to upgrade to composite or LED.
Replacement sealed beam units must carry approval marking. The original specification on most UK and EU-supplied sealed beams is an E mark (E1, E2, E11 etc), an ECE marking (R1 or R5 for sealed beams), or for older US units a SAE marking accepted by the C&U Regulations for vehicles registered before 1986.
LED retrofit units fitted in a sealed beam housing sit in a more complicated legal position. The DVSA position, set out in MOT testing guidance, is that any headlamp on a vehicle must produce an acceptable beam pattern with a clear cut-off, must not dazzle other road users, and must not show a colour other than white or selective yellow. An LED retrofit that meets these conditions passes the MOT.
The grey area covers ECE and E-mark approval on the retrofit unit itself. Many LED sealed beam replacements sold in the UK carry no ECE approval, because the original sealed beam socket is not designed for an LED light source under any approval regulation. A strict reading of C&U requires the replacement to carry approval. A practical reading, supported by the MOT pass-on-beam-pattern test, allows the retrofit if the beam is acceptable.
The clearest legal position uses LED sealed beam replacements that carry ECE R112 or DOT SAE J581 approval. JW Speaker, Truck-Lite, Hella and Lucas all sell ECE-approved 7 inch and 5 3/4 inch LED sealed beam replacements that comply directly.
Like-for-Like Sealed Beam Replacement
Replacing a sealed beam with another sealed beam is the simplest route. The new unit slots into the existing bezel, connects to the existing three-prong wiring and works without any adaptation.
Sources for genuine sealed beam replacements include classic tractor parts dealers, Hella’s classic range, Lucas Classic, and US suppliers shipping to the UK. A 7 inch round Type 2 halogen sealed beam (dipped plus main) costs GBP 18 to GBP 45 from these sources. A Type 1 main-beam-only unit costs GBP 12 to GBP 25.
The replacement procedure takes 10 to 15 minutes per lamp:
- Disconnect the battery
- Remove the bezel screws (typically three Phillips or slotted screws)
- Lift the bezel away and free the retaining ring
- Pull the sealed beam forward and unplug the three-prong connector
- Plug the new unit onto the connector
- Fit the new unit into the retaining ring
- Replace the bezel and screws
- Reconnect the battery and test
A like-for-like halogen sealed beam delivers 700 to 1,200 lumens on dipped beam and 1,200 to 1,800 lumens on main beam. The figures match what the tractor produced when new, which suits a vehicle being kept original or used only occasionally.
LED Conversion in a Sealed Beam Housing
An LED conversion in a sealed beam housing replaces the original glass-and-filament unit with a modern LED lamp built to the same overall dimensions and connector pattern. The conversion delivers 3 to 5 times the lumen output at a fraction of the current draw, with no other change to the tractor.
LED sealed beam replacements come in two forms. The first is a one-piece LED lamp shaped like a sealed beam, with the LED chips, the reflector and the lens built into a single unit. The unit slots into the original bezel and plugs into the three-prong connector. The second is a housing-plus-bulb kit, where the housing accepts an H4 LED bulb in a separate socket.
A typical LED 7 inch sealed beam replacement delivers 4,000 to 6,000 lumens at 30 to 50 watts. Current draw on 12V runs at 2.5 to 4 amps per lamp, against 5 to 8 amps for a halogen sealed beam of equivalent output. The lifespan reaches 30,000 to 50,000 hours against 500 to 1,000 hours for halogen.
The colour temperature for an LED sealed beam runs at 5,000 to 6,500 Kelvin (daylight white). The original halogen sealed beam ran at 2,800 to 3,200 Kelvin (warm yellow). The cooler LED light improves contrast in night driving but changes the look of a restored classic tractor noticeably.
Wiring and Connector Adaptation
Most LED sealed beam replacements fit the original three-prong connector with no rewiring. The three prongs carry ground, dipped beam and main beam, and the LED unit uses the same pin assignment.
A few LED conversions need adapter pigtails. The most common situation is a tractor wired with the dipped and main beam connections reversed from the US standard. The adapter pigtail swaps the pins to match the LED unit. The pigtail costs GBP 3 to GBP 10 and plugs in line between the tractor loom and the LED lamp.
Older 6V tractors (Ford 8N and 9N from 1939 to 1952, Massey 35 and earlier from before 1959, some International Harvester models) need either a 6V LED unit or a 12V conversion of the whole electrical system. A 6V LED sealed beam replacement exists but the choice is narrow. Most 6V tractors keep their sealed beam headlights as part of a period restoration.
24V tractors and commercial vehicles need 24V LED units or multi-voltage units. ABL, Hella and JW Speaker make 9V to 32V LED sealed beam replacements that fit both 12V and 24V systems without modification.
Tractors Still Running Sealed Beams
Many classic and heritage tractors still on UK farms run sealed beam headlights. The list covers tractors from the 1950s through to the early 1990s.
John Deere: 4020, 4030, 4040, 4230, 4240, 4430, 4440, 4630, 4640, 4840, 8430, 8440, 8640 (1960s to 1980s)
Massey Ferguson: 35, 65, 135, 165, 175, 240, 290, 390, 690, 1100, 1135, 1150, 1155, 2705, 2745, 2775 (1959 to mid-1980s)
Ford and New Holland: 8N, 9N, NAA, 600, 800, 4000, 5000, 6000, 7000, 8000, 9700, TW series (1939 to 1985)
International Harvester: B250, B414, Farmall 240 to 1466, 66 series, 86 series (1956 to early 1980s)
David Brown: Cropmaster, 770, 880, 990, 1200, 1212, 1290, 1390, 1394, 1494, 1594 (1950s to 1980s)
Case: 470, 570, 770, 870, 970, 1070, 1270, 1370, 1570 (1969 to 1978)
Restored vintage tractors from Field Marshall, Fordson, Nuffield, Allis-Chalmers and Oliver also commonly run sealed beams from the same era.
Best LED Replacement Picks
The right LED sealed beam replacement depends on whether the tractor is for daily work or for occasional restoration use.
Daily-work pick for 7 inch round: JW Speaker Model 8700 Evolution 2, 4,800 lumens, ECE R112 approved, multi-voltage 9-32V, GBP 220 to GBP 280 per pair. ECE approval gives complete legal compliance.
Mid-budget pick for 7 inch round: Hella 7 inch LED, 3,800 lumens, ECE approved, 12V or 24V, GBP 110 to GBP 160 per pair. A practical balance of output, compliance and cost.
Budget pick for 7 inch round: Generic LED sealed beam replacement, 3,000 to 4,500 lumens, no ECE approval but acceptable MOT beam pattern, GBP 30 to GBP 60 per pair. Suits off-road and yard use, MOT pass depends on beam pattern at the test.
5 3/4 inch round pick: Truck-Lite 7160 LED, 1,800 lumens dipped or 3,000 lumens main, ECE approved, 12V or 24V, GBP 90 to GBP 140 each. Made specifically for the smaller round size.
Rectangular pick: Hella LED 4 x 6 or 5 x 7, 2,500 to 4,000 lumens, ECE approved, GBP 80 to GBP 140 each. Direct fit to existing rectangular bezels on 1980s US-built tractors.
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