Rear fog lights should be used only when visibility is very poor, specifically when it drops below about 100 meters (328 feet), such as during thick fog, heavy rain, or snow. These lights are designed to make your vehicle more visible to drivers behind you in these low-visibility conditions by shining a bright red light that cuts through the gloom. They should not be used in normal driving conditions or light mist as they can dazzle or distract other drivers and obscure the brake lights, increasing the risk of accidents. Once visibility improves beyond this poor range, rear fog lights must be turned off to avoid causing glare to other road users. Using them improperly can also result in fines in regions where regulations apply. In summary:
- Use rear fog lights only when visibility is below 100 meters, such as in dense fog, heavy rain, or snow.
- Turn them off as soon as visibility improves.
- Avoid using them in normal weather to prevent dazzling others and obscuring brake lights.
- They are a safety device to prevent rear-end collisions by increasing your car’s visibility in poor conditions.
This guidance is supported by the Highway Code and multiple vehicle safety sources.
