Fog Lights: Functions and Rules

Fog lights are used to illuminate a motor vehicle in particularly poor visibility conditions caused, for example, by fog, rain, or snow. They are mounted below the headlights. Together with equipment features such as a parking heater, fog lights are a useful piece of autumn and winter equipment. They are usually located slightly below the main headlights. The fog lamp is mounted low on vehicles to provide additional light in poor weather conditions.

In the UK, fog lights are an option, while a rear fog light is compulsory. Since 2011, daytime running lights (DRL) have been mandatory on new cars. LED fog lights can be used as daytime running lights, as long as they have a proper dimming feature and are symmetrically mounted on the front of the vehicle.

When should you use your fog lights

It is mandatory that you use the headlights when the visibility is greatly impaired, for example, when you cannot see more than 328 ft. in front of you. You are allowed to use the fog lights as well, but must turn them off when visibility is improved. Using them together with the low beam makes little sense, as a wider illumination is only achieved at close range. The dangerous glare for the driver, which is caused by dense fog, is not minimised with this lighting combination. This glare can occur in foggy conditions, for example. The fine water droplets reflect the light that hits them and can dazzle the driver. In this case, the low beam creates too much scattered light at the driver’s eye level. The fog lights, on the other hand, illuminate the area below their mounting height and thereby prevent glare.

Do not turn them on unless you have to; the UK highway code states that you must not use them unless there is a serious reduction in visibility. 

How to turn them on

On some cars the buttons are located on the side of the steering wheel, while on others they are on the indicator lever, which you have to turn in order to switch them on. There may be slight variations, depending on the make and model of your car, so be sure to refer to the owner’s manual for specific instructions.

Rear fog lights

In the UK, these  must be mounted in the middle or at the rear of the vehicle . A rear fog lamp is a focused light and must be fitted at right angles to the rear of the car. They can make it a lot easier to spot a vehicle in front of you when you are driving in foggy conditions. Don’t be tempted to use the lights of other cars as a reference, as these can give you a false sense of security.

Are yellow fog lights legal in the UK

Both white and yellow are allowed in the UK. Yellow lights do have their advantages, particularly in the winter months when you could have problems with visibility due to the weather. The dark yellow is less dazzling than the white, because it has a cooler Kelvin temperature and a higher wavelength than white light. The longer wavelengths can enhance visibility since the light is more refracted and so travels farther, but they do not necessarily improve visibility. They reflect less water particles and so don’t dazzle you, or the oncoming traffic, as much.