This is when to switch on the fog lights in your car - and how to do it

Monday, 7th December 2020, 4:25 pm
Updated Monday, 7th December 2020, 4:25 pm

As temperatures drop during the winter months, the sight of fog and mist in the morning becomes more common.

Commuters, runners and dog walkers across the country can be seen enduring icy temperatures in low levels of light.

And, with colder temperatures forecast in the run up to Christmas, many will be reaching for hats, scarves and thermal underwear to keep the cold at bay.

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But why does it get foggy - and is it the same as mist?

What causes fog?

Fog is essentially a cloud at ground level that causes a reduction in visibility, according to the Met Office.

It is caused by tiny water droplets suspended in the air and is one of the most common weather conditions across the UK.

Fog is often worse or thicker in industrial areas like towns and cities due to pollution. Pollution particles allow more water droplets to form.

However, frequent visitors to the countryside will also often see fog enveloping the hills and moors, making for a picturesque winter’s scene.

How does fog differ from mist?

Mist is typically not as thick as fog.

It is formed in the same way through tiny water droplets in the air but is much quicker to dissipate, like when you can see your breath on a cold day or when your glasses steam up.

The difference between fog and mist is its density - typically you can see further into the distance when it’s misty. Fog is technically when you can see less than 1,000 metres away.

What is freezing fog?

Freezing fog occurs when the land cools under clear skies, typically through the night, as temperatures delve below freezing.

Without clouds to keep the earth's warmth in, the heat escapes into space and leaves the surface of our planet much cooler.

This means the tiny water droplets in the air remain as liquid and only freeze when they meet a surface. When this happens, a white deposit of feathery ice crystals known as rime forms.

How do I turn on my fog lights?

Because of the reduced visibility of fog, vehicles are fitted with fog lights which help drivers see more clearly during the weather phenomenon.

Fog lights are often found on the same stalk as the main headlights. The lights can be turned on and off by twisting a part of the stalk.

Yet consult your car's handbook as turning them on and off can change depending on the make and model of the car.

When should I use fog lights?

When visibility is poor, you should use your fog lights alongside dipped beam headlights, not as an alternative. A good rule of thumb is to use your fog lights if you can't see the rear lights of the car in front.

However, you should only use fog lights when there is fog as the strength of the beam can dazzle other drivers.

A symbol will appear on the car's dashboard when the fog lights are turned on.