The rules of using your car light

Key takeaways

• During the day use headlights and fog lights in poor visibility, but turn them off when visibility improves

• Use headlights at night, but dip them in built-up areas or when near other road users

• Check brake lights weekly and replace faulty bulbs immediately

• Windscreens must let at least 75% of light through; front side windows must let 70% through

It may be a while since you’ve taken your driving test, so there’s no better time than now to brush up on the rules and regulations surrounding car lights. 

Here’s all you need to know about headlights, sidelights and registration plate lights, as well as windscreens and other windows.

Lights – daytime rules

You might think it’s only important to use lights at night, but there are also instances when you should use them during daylight hours. 

Brake lights should come on when you hit the foot brake, but not used continuously in stationary queues of traffic – it causes unnecessary glare for drivers behind you. 

Headlights and fog lights should also be used in daytime hours when visibility is seriously reduced – although you must switch them off when visibility improves to avoid dazzling other road users. Dipped headlights should be turned on to ensure you can be seen in dull weather. 

All sidelights and rear registration plate lights must also be lit between sunset and sunrise, even if it still seems light enough to manage without them. 

Under EU rules, since 2011 all new cars are required to have daytime running lights that come on automatically when the engine is started, and which turn off automatically when headlights or sidelights are lit (these still need to be used as outlined above). Your daytime running lights only apply to your headlights and your rear lights won't come on automatically - so remember to switch on your lights as it starts to go dark. We explain further, below. 

Lights – nighttime rules

If driving at night, you need to have sufficient light to see clearly where you are going, and to ensure that you can be seen, while not dazzling other road users. 

To this end, you must always use your headlights at night (half an hour after sunset and half an hour before sunrise), but you must ensure that they are dipped in built-up areas or when you are behind or approaching other road users, including pedestrians, cyclists and horse riders. 

When overtaking, for example, you should always keep your headlights dipped until you are level with the other vehicle and then change to main beam if necessary, unless this would dazzle oncoming road users. 

If you are on the receiving end of dazzling headlights, meanwhile, you should slow down, or if necessary stop, and only continue once you can see the road ahead properly. 

Although you can legally just use your sidelights at night if you're driving under 30mph in a well-lit area, most drivers use dipped headlights anyway for better visibility of the road ahead.

Brake lights

As far as your brake lights are concerned, make sure they’re working and keep them clean.

As well as the safety issues, you’re likely to get pulled over sharpish if something isn’t working. If you do get pulled over by the police you may just get a verbal warning, but you could also get:

• a fixed penalty notice - a £60 fine and three points on your licence

• a Vehicle Defect Rectification Notice - 14 days to fix the fault and provide proof of the fix

• your car taken off the road immediately

It can also be extremely dangerous if you have a dodgy brake light - if one or both brake lights aren't working, the cars behind won't be able to tell when you're slowing down, especially if you brake suddenly. 

You should check your brake lights at least once a week by getting someone to stand behind your car while you apply the brakes, and replace any faulty bulbs straight away. 

You should also check your indicator lights at the same time and replace any that are faulty. 

Hazard lights

Hazard warning lights should only be used when your vehicle is stationary (perhaps due to breakdown) to warn that it is temporarily obstructing traffic or is in a hazardous or dangerous location. They should never be used as an excuse for dangerous or illegal parking. 

The only exception to this rule is when you are driving or being towed on a motorway or unrestricted dual carriageway and you need to warn drivers behind you of a hazard or obstruction ahead.  

Fog lights

Driving in fog is no fun at all as visibility can be reduced to just a few feet, so all cars are fitted with at least one rear extra light to make them more visible in fog. 

Some cars are also fitted with front fog lights. 

Although it's not a legal requirement to use your fog lights if you're driving in fog, it’s much safer to so that other motorists can see you. 

Never use your fog lights when visibility is clear though, especially at night when other drivers can easily be dazzled. 

Not only is this dangerous, it's also illegal and could result in a non-endorsable Fixed Penalty Notice, which is a £50 fine but no penalty points

Windows

Whatever the time of day, if you can’t see out of your windscreen, your headlights aren’t going to help you much. 

That’s why the government insists that drivers with tinted windows have glass that lets at least 75% of light through the front windscreen and 70% through the front side windows.

However, there are no rules about how much light tinted rear windscreens or rear passenger windows must allow through. 

If you break this rule, not only do you risk invalidating your insurance policy, you could also have your vehicle seized. 

It’s also worth noting that windscreen cracks in the driver’s line of vision and larger than 10mm, as well as those elsewhere of more than 40mm in length, can cause a car to fail its MOT. Driving around with a significant crack in your windscreen could be considered a motoring offence. 

Also make sure you keep your windows clean on the inside and out, especially over the winter months, to help minimise sun glare.