Headlights and Bulbs: Checks for Dark Winter Evenings

Written by Petro Olekhnovych, mobile mechanic in Aylesham, Kent

Why winter is when lights matter most

From November to February most commutes start or finish in the dark. Many of the roads around Aylesham, Wingham and Shepherdswell have no street lighting at all, and coastal fog around Deal and Dover can cut visibility quickly. Your headlights have to show you the road and also show other drivers where you are.

Winter also brings dirt. Salt spray from the A2 and A256 coats lenses with a film that can cut light output noticeably. Wiping the lenses when you clear the windows is a small habit that makes a real difference, and Highway Code rule 229 already expects you to keep lights clean and visible before you set off.

The five-minute driveway check

Park facing a wall or garage door if you can, so you can see the beam pattern. Then:

1. Switch on sidelights and check front, rear and number plate lights.
2. Switch to dipped beam and check both sides light up equally on the wall.
3. Flick to main beam and check both work.
4. Check all four indicators and the hazard lights.
5. Check front and rear fog lights if fitted.
6. For brake lights, ask someone to press the pedal, or reverse up to a window or garage door at night and look in the mirror.
7. Check reversing lights with the ignition on, handbrake set and reverse selected, engine off.

A bulb warning on the dashboard is helpful, but not every car has one for every lamp, so do not rely on it alone.

Why headlights go dim

If the lights work but seem weak, look at these causes in order:

• Cloudy or yellow lenses: plastic headlight covers degrade in sunlight. The light behind them is fine, but much of it is scattered.
• Ageing bulbs: halogen bulbs lose brightness before they finally blow.
• Moisture inside the unit: condensation or water inside a headlight suggests a failed seal or a cracked housing, which is common on cars kept near the sea.
• Poor earth or corroded connectors: one dim light and one bright light often points to wiring.
• Low charging voltage: if all lights dim at idle and brighten with revs, the battery or alternator needs testing.

What fails an MOT

The MOT inspection covers lamps, reflectors and electrical equipment. Common bulb related failures include:

• Any required lamp not working, including a single number plate bulb
• Headlight aim too high, too low or to one side
• Damaged lenses that let out white light where it should be red, or let water in
• The wrong colour bulb, such as a blue-tinted bulb in a headlight
• Warning lights that indicate a lighting fault

Lights are among the most common reasons for a failure, which is why they are on every pre-MOT check we do. You can see the other usual failures in our guide to common MOT failures.

Bulb changing: when to do it yourself

On many older cars a headlight bulb is a two-minute job from behind the unit. On a lot of modern cars it means removing the battery, an air box or part of the wheel arch liner. Handle halogen bulbs by the base, as oil from your fingers shortens their life. Xenon or HID headlamps use high voltage, so leave those to someone with the right knowledge. LED headlights are often sealed units that cannot be repaired with a simple bulb.

If a bulb keeps blowing, the cause may be a wiring or voltage fault rather than bad luck.

How we can help

We check every light on the car at your home as part of our pre-MOT and winter checks, look for water in the units, test charging voltage and diagnose repeat bulb failures. Many bulbs can be swapped at the car, and if a unit is sealed or the job needs more work, we will tell you honestly what is involved. Labour is £30 to £50 per hour, and we quote before starting. Message us your reg on WhatsApp 07563 350335 or via our contact page. Before winter, our winter car checklist is also worth a look.

Frequently asked questions

Is a blown bulb an MOT fail?

Yes. Lamps that do not work, are the wrong colour or are badly aimed are MOT failures, and that includes number plate lights and brake lights. A bulb is usually a simple fix, so it is worth checking before the test.

Should I replace headlight bulbs in pairs?

It is a good idea. Bulbs of the same age tend to fail close together, and a new bulb next to an old one gives uneven light.

Why do my headlights look dim even with new bulbs?

Cloudy, yellowed lenses, a poor earth connection or low charging voltage can all reduce light output. The lens is the most common culprit on cars over about eight years old.

Can I be stopped for a blown headlight?

Yes. Driving with a defective light can lead to a police stop and a fixed penalty or a vehicle defect notice, so it is worth fixing quickly.

Sources

• The Highway Code, GOV.UK
• MOT inspection manual for cars and light vans, GOV.UK