When must I use dipped headlights in the UK?

The Highway Code sets three requirements. You must have your sidelights and rear registration plate lamp lit between sunset and sunrise. You must use headlights at night, except on a road that has lit street lighting, which is generally a road subject to a 30 mph limit. And you must use headlights whenever visibility is seriously reduced, at any time of day. Night for this purpose means the period from half an hour after sunset to half an hour before sunrise. In practice the safe habit is dipped beam whenever the light is poor, lit road or not.

Are headlights checked in the MOT?

Thoroughly. The tester checks that each headlamp is present, secure, the correct colour and working, that the lens is not damaged in a way that affects the light emitted, that the switch operates from the driver's seat, and that the aim is within the permitted limits using a beam setter. Headlamp aim is one of the most common failures in the whole test, partly because it drifts slowly and partly because it changes when suspension sags, a heavy load sits in the boot, or a bulb is refitted slightly differently. It is also one of the quickest and cheapest things to correct before a retest.

What is the difference between dipped beam and sidelights?

Dipped beam is a proper driving light that puts a shaped, aimed beam on the road ahead while keeping the cut-off below oncoming drivers' eyes. Sidelights, properly called front and rear position lamps, are low-power lamps whose only job is to make the car visible to others — they light nothing. You can drive on sidelights only in very limited circumstances and it is almost never a good idea. The tell-tales differ too: sidelights show a pair of small lamps facing outwards, dipped beam shows the headlamp outline with downward-sloping lines.

Why are my headlights dim even though the bulbs work?

Usually the lens rather than the bulb. Modern headlamps are polycarbonate with a thin protective coating, and once that coating breaks down the plastic hazes, yellows and scatters light instead of projecting it, which can halve what reaches the road. Halogen bulbs also dim substantially over their life without ever failing outright, so a pair that has done several years is worth replacing together. Poor earths and corroded connectors are the third common cause. If the lenses are badly clouded a tester can record it as a defect where the emitted light is adversely affected.

Dashboard warning light

Dipped beam warning light

Last updated 27 July 2026

Quick answer

Dipped beam headlamps are on. Green means working, not faulty, and no action is needed. It is the same headlamp outline as the blue main beam symbol, but green and with the beam lines angled downwards.

What to do: No action needed
Can you drive?: Yes

Why it is green

Confirms something is switched on and working. Not a fault.

What turns it on

Turning the light switch to the headlamp position, or an automatic system deciding it is dark enough. On many modern cars the tell-tale is small and easy to miss, which is why people so often drive on daytime running lamps alone in poor weather without realising the rear of the car is unlit.

What to do about it

Use dipped beam between sunset and sunrise, and whenever visibility is seriously reduced during the day. Rain, spray, fog and low winter sun all count.
Do not rely on daytime running lamps in bad weather. They light the front of the car only, so a car on DRLs in heavy spray is invisible from behind.
Check the beam pattern occasionally against a wall or a garage door. Headlamp aim is one of the most common MOT failures and a beam that has dropped or climbed is very hard to notice from the driver's seat.
Clean the lenses. Fogged, crazed or yellowed polycarbonate headlamps cut light output badly and can fail the test if the light emitted is adversely affected.

Can you keep driving?

Yes

Yes. A green tell-tale is confirmation that dipped beam is on, which in most British driving conditions is exactly where you want it. If anything, this is a lamp people should see more often than they do.

What causes it

The headlamp switch is in the dipped beam position
Automatic headlamp control has switched them on because the light sensor sees low ambient light
On some cars the tell-tale also lights when main beam is selected, alongside the blue lamp

Does it fail an MOT?

Not on its own — but what causes it often does.

There is no MOT defect for the dipped beam tell-tale itself — the only mandatory lighting tell-tales are main beam, rear fog, indicators and hazards. The headlamps behind it, though, are among the most heavily tested items on the car. Section 4.1 covers presence, condition, security, colour and operation; section 4.1.2 covers headlamp aim, which is a major defect if the beam image is outside the permitted limits and is one of the most common reasons cars fail; and section 4.1.3 covers the switch, which must work from the driver's seat.

Common questions

When must I use dipped headlights in the UK?: The Highway Code sets three requirements. You must have your sidelights and rear registration plate lamp lit between sunset and sunrise. You must use headlights at night, except on a road that has lit street lighting, which is generally a road subject to a 30 mph limit. And you must use headlights whenever visibility is seriously reduced, at any time of day. Night for this purpose means the period from half an hour after sunset to half an hour before sunrise. In practice the safe habit is dipped beam whenever the light is poor, lit road or not.
Are headlights checked in the MOT?: Thoroughly. The tester checks that each headlamp is present, secure, the correct colour and working, that the lens is not damaged in a way that affects the light emitted, that the switch operates from the driver's seat, and that the aim is within the permitted limits using a beam setter. Headlamp aim is one of the most common failures in the whole test, partly because it drifts slowly and partly because it changes when suspension sags, a heavy load sits in the boot, or a bulb is refitted slightly differently. It is also one of the quickest and cheapest things to correct before a retest.
What is the difference between dipped beam and sidelights?: Dipped beam is a proper driving light that puts a shaped, aimed beam on the road ahead while keeping the cut-off below oncoming drivers' eyes. Sidelights, properly called front and rear position lamps, are low-power lamps whose only job is to make the car visible to others — they light nothing. You can drive on sidelights only in very limited circumstances and it is almost never a good idea. The tell-tales differ too: sidelights show a pair of small lamps facing outwards, dipped beam shows the headlamp outline with downward-sloping lines.
Why are my headlights dim even though the bulbs work?: Usually the lens rather than the bulb. Modern headlamps are polycarbonate with a thin protective coating, and once that coating breaks down the plastic hazes, yellows and scatters light instead of projecting it, which can halve what reaches the road. Halogen bulbs also dim substantially over their life without ever failing outright, so a pair that has done several years is worth replacing together. Poor earths and corroded connectors are the third common cause. If the lenses are badly clouded a tester can record it as a defect where the emitted light is adversely affected.

This is general guidance, not a diagnosis. Manufacturers draw the same system differently and reuse symbols for more than one function, so check the handbook for your own car before acting on anything here.

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