Why is it dangerous to leave rear fog lights switched on after the fog has cleared?

If your rear fog lights are left on when it isn’t foggy, the glare they cause makes it difficult for road users behind to know whether you’re braking or you’ve just forgotten to turn off your rear fog lights. This can be a particular problem on wet roads and on motorways. If you leave your rear fog lights on at night, road users behind you are likely to be dazzled and this could put them at risk.