Swapping halogen headlight bulbs for LED is one of the most popular upgrades on cars built in the last twenty years: whiter light, more of it, and a bulb that typically outlasts the car. It is also one of the easiest upgrades to get wrong. The bulb must have the right fitting, the right electronics for your car's CANbus system, and the right beam pattern for your headlamp housing. This guide covers all three, plus what the law allows.
Step 1: identify the fitting
The fitting (or base) is the shape of the bulb's connector and locating tabs. Your car takes one specific fitting for dipped beam and may take a different one for main beam. The quickest ways to find yours:
- Look at the old bulb — the fitting is usually printed on the base (for example “H7 12V 55W”).
- Check the owner's handbook under “bulb specifications”.
- Send us your VIN or registration and we will tell you.
The common fittings and where you will find them:
- H7 — the most common dipped-beam bulb on European cars from around 1995 onwards (VW, Audi, BMW, Mercedes, Ford, Vauxhall, Peugeot and many more).
- H4 — a dual-filament bulb that does dipped and main beam in one. Common on smaller and older cars, vans and many Japanese models.
- H11 / H8 / H9 / H16 — similar L-shaped bulbs used for dipped beam, main beam or fog lights on many Japanese, Korean and American cars and newer European models.
- HB3 (9005) / HB4 (9006) — common on Toyota, Honda, Lexus, Subaru, Mazda and many US-market cars.
- H1 and H3 — older single-filament fittings, often used for main beam and fog lights.
H8, H9, H11 and H16 look almost identical and some are interchangeable in practice, but the correct one is the one your handbook lists — the power rating and tab positions differ.
Step 2: CANbus and “bulb out” errors
Most cars built after about 2005 monitor the headlight circuit. A halogen bulb draws around 55 W; an LED bulb draws a fraction of that, so the car can think the bulb has blown and show a warning, flicker the LED, or refuse to power it. There are two fixes:
- CANbus-ready LED bulbs with built-in load resistors or smart drivers that mimic a halogen load. These work on the majority of cars.
- External decoders (warning cancellers) wired between the bulb and the connector for cars with stricter monitoring — typically BMW, Mercedes, Audi, VW, Jeep and Dodge.
Our listings state whether a bulb is CANbus-ready and which vehicles need a decoder, so you do not find out after fitting.
Step 3: beam pattern and glare
A halogen headlamp is designed around a filament in one exact position. A good LED bulb places its LED chips on both sides of a thin board in the same position as the filament, so the reflector or projector produces the same cut-off line and the same spread. A cheap LED bulb with chips in the wrong place throws light above the cut-off and dazzles oncoming drivers while lighting the road worse than the halogen it replaced. Look for bulbs that specify a halogen-style chip layout, a 360° rotatable collar so you can align the chips horizontally, and a fan or heat-sink that actually fits inside your headlamp's dust cover.
Colour temperature and lumens
Halogen is about 3,200 K (warm white). Most LED headlight bulbs are 6,000–6,500 K (cool white), which looks modern and matches factory LED and xenon lights. Avoid anything above 6,500 K — blue-tinted light reduces contrast in rain and is more likely to attract attention from the police. Lumen figures on packaging are often quoted per pair and at the chip rather than at the road; a realistic good-quality bulb delivers around 1,500–2,500 lm per bulb.
Is it legal?
This depends on where you drive, and it is important to be honest about it. In the UK, fitting an LED bulb into a headlamp designed for halogen is generally not road-legal, and MOT guidance since 2021 states that a halogen headlamp unit converted to LED should fail unless the unit is designed for it. A small number of LED bulbs now carry type approval for specific vehicles in certain countries (Germany was first), and that list is growing. Before you buy, check the approval status for your car and country; otherwise treat LED retrofit bulbs as for off-road, show or track use. Factory-fitted LED headlamps are a different matter and are fully legal — the rules are about converting a halogen unit.
Fitting tips
- Switch the lights off and let the old bulb cool before removing it.
- Do not touch the LED board or lens with bare fingers.
- Rotate the collar so the LED chips sit at 3 and 9 o'clock (horizontal) in the housing.
- Make sure the dust cover closes; if it will not, you need a shorter bulb or an extended cover, not an open housing.
- Check the beam against a wall at 5–7 metres before driving at night.
Every LED headlight bulb at AVT Expert is listed with its fitting, CANbus compatibility, lumens, colour temperature and the vehicles it suits. Send us your VIN or registration if you want the fitting confirmed first. Browse LED headlight bulbs.