Headlights aimed outside the permitted limits can cause a car to fail its MOT.
The MOT inspection manual also treats an obviously incorrect beam pattern as a major defect.
The checks come amid guidance from the Department for Transport (DfT) on reducing headlight glare, which can dazzle other road users.
The Highway Code says drivers must not use lights in a way that dazzles or causes discomfort to others, including pedestrians, cyclists and horse riders, the department says.
MOT rules for certain replacement bulbs changed on October 14, 2026.
The Driver and Vehicle Standards Agency (DVSA) says testers must accept ECE-approved LED replacement bulbs, known as LEDr bulbs, in compatible halogen headlamp units.
The change applies to class 3, 4, 5 and 7 vehicles with existing halogen headlamps fitted with approved LEDr bulbs.
The bulb must be approved for use in that lamp and have a corresponding manufacturer-issued approval sticker, the MOT manual says.
The sticker must be permanently fixed to the vehicle and visible to the tester.
A headlamp must be failed if the required sticker is missing, unreadable, appears to have been tampered with or clearly does not match the bulb fitted.
The DVSA says the change does not apply to class 1 and 2 motorcycles, halogen units converted to high intensity discharge bulbs, or full LED headlamp replacements.
Complete replacement headlamp units manufactured with LED or high intensity discharge light sources are subject to the other relevant MOT requirements, the inspection manual says.
In its guidance on glare, the DfT advises drivers to dip their lights before passing other vehicles or road users and be ready to override automatic lighting controls.
A heavy load can alter the beam level, so drivers should consider adjusting it for passengers, luggage or a trailer if the vehicle does not do so automatically.
The department also recommends keeping lenses clean and using fog lamps only when visibility is significantly reduced, switching them off when conditions improve.
Headlamp aim can move out of alignment before a vehicle's first MOT, so the DfT suggests considering an earlier check.
Its guidance says: "Do not fit non-approved bulbs or light sources. These may alter the beam pattern, breach regulations or invalidate insurance."
Drivers are also told not to rely on daytime running lamps alone at night or in low light, and to make sure headlights are switched on.
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