The plastic lens has gone cloudy, yellowed or cracked to the point that it scatters the beam. Testers judge it on light output and beam pattern, not on looks, so a slightly dull lens usually passes while a heavily fogged one that softens the beam cut-off doesn't.
Wording as it commonly appears on an MOT certificate: “Headlamp lens deteriorated or damaged so the light output is affected”.
What does it mean?
The plastic lens has gone cloudy, yellowed or cracked to the point that it scatters the beam. Testers judge it on light output and beam pattern, not on looks, so a slightly dull lens usually passes while a heavily fogged one that softens the beam cut-off doesn't.
How serious is it?
Usually recorded as: Minor, Major. The tester assesses the actual vehicle on the day, so your certificate is what counts.
What normally causes it?
- UV breaking down the factory hard coat on the polycarbonate lens — normal on any car past about eight years
- Stone chips and motorway sandblasting
- A crack letting water in, which then mists the inside where polishing can't reach
- Previous restoration done without re-sealing a UV coat, which hazes again within months
What a mechanic would check
I look at the beam on the aim board rather than at the lens. If the cut-off line is fuzzy and the hot spot is weak, the lens is the problem. Then I check whether the haze is on the outside — wipe it with a wet cloth and if it clears momentarily, a proper restoration will work; if it's misted inside, the unit is the fix.
What might need replacing
- Professional headlamp restoration with a UV-stable sealer
- A headlamp unit
- A headlamp aim reset afterwards
Can you still drive it?
Legal to drive, but you'll notice how much less you can see on unlit roads. Worth sorting before winter regardless of the MOT.
Repair cost
Restoration is far cheaper than a new unit and works well when the damage is external. Cheap polish-only kits haze back quickly — the UV coat is what makes it last.
Before the retest
Walk round the car with someone working the switches: dipped, main, sidelights, indicators, hazards, brake lights including the high-level light, rear fog and number plate lamps. A new headlamp bulb or unit should be followed by a beam aim check, because a correctly working lamp aimed into oncoming traffic still fails. Wipe lenses clean and make sure no warning lights stay on after start-up.
Retest rules
If the vehicle stays at the test centre for repair and is retested within 10 working days, a partial retest is often free; some items qualify for a free retest if you bring the car back by the end of the next working day. The exact conditions are set out on GOV.UK, so confirm with the test centre before you leave. A major or dangerous failure means the car cannot legally be driven away unless the previous MOT is still valid and nothing dangerous was recorded — check your certificate first.
Related help
More lights failures · MOT failure decoder · Ask a mechanic about your certificate
This is general guidance from a UK mechanic, not a substitute for a physical inspection. Only the tester who inspected your vehicle can confirm what was recorded and why.