Who needs help understanding how to use fog lights? After all, it seems obvious - fog lights are for turning on when it’s foggy.

But it’s not so simple. You may often see cars with their fog lights turned on when they’re not needed, or vice versa.

When do you turn them on?

It’s not always clear when fog lights are needed.

Much of the answer comes down to the fine difference between fog and mist? The Met Office says if visibility is less than 1,000 metres, then it’s foggy. If visibility is greater than 1,000 metres, then it’s misty.

From a driver’s perspective the important thing to know is to turn on your fog lights, as well as your dipped headlights, when visibility falls to 100m (328 feet) or less. That is the equivalent to the length of a football pitch. So you need a reasonably thick fog before you turn them on.

That’s because the purpose of fog lights is to help make your car visible to others, rather than enabling you to see further in the fog.

Do all cars have fog lights?

Rear fog lights are required by law on all cars in the UK.

Front fog lights are more likely to be found as an extra on higher specification models. Auto Express says some newer cars have foregone front fog lights in favour of daytime running lights (DRLs). These are the bright LED lights you see on all new cars, which are permanently on and are designed to make the cars more visible to other road users.

How do I use them?

If you aren’t sure how to turn your fog lights on or off - perhaps because you have a new car or simply haven’t had them on for several months and have forgotten – spend a few moments to get to grips with them. That way you won’t suddenly have to figure it out one bleak winter’s morning when you’re in a rush.  

Check your car’s manual if in doubt, but fog lights are normally operated by a separate switch from the main light controls. A dash light will usually come on to let you know the fog lights are on.

And if your car has automatic lights, don’t assume your fog lights will come on automatically too.

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What if I forget?

It’s dangerous not to have fog lights on when they’re really needed. There were 16,406 accidents in rain, sleet, snow or fog on Britain's roads in 2017, including 205 fatal incidents, according to figures from the Department for Transport.

Why turn fog lights off?

Judging by the number of drivers who keep their fog lights on even when conditions are clear, not many people are aware of the importance of turning them off. Misuse of fog lights can result in a fine of £30.

The Highway Code is very clear about this. It says:

You must not use front or rear fog lights unless visibility is seriously reduced as they dazzle other road users and can obscure your brake lights. You MUST switch them off when visibility improves.

What else should I do when driving on foggy days?

Turning on fog lights is a good start. But there are other precautions you can take.

This includes slowing down and keeping your distance from the car in front of you.

If it’s a real pea souper out there, the RAC recommends you wind down your windows at junctions and crossroads to allow you to listen out for approaching traffic. But if conditions are that extreme, you may want to park safely and wait until the weather improves to continue.

And of course, switch off your fog lights when the fog clears.

To read more about road safety go to Solved.