Fog lights have a low, flat, wide beam to illuminate the road below the fog or mist. They must be wired to switch on separately to the high-beam and low-beam headlights. Front fog lamps may emit a white or yellow coloured light.
Rear fog lights have a higher intensity light used on a vehicle to make it more easily visible from the rear in dense fog. Rear fog lights may only emit a red light. However, rear fog lights appear similar to brake lights and, when used inappropriately, may mislead other drivers into thinking that the brakes are constantly being applied.
Front or rear fog lights must not be used unless driving in fog or other hazardous weather conditions causing reduced visibility. This may include snowfall, heavy rain or a dust storm. During the day when there is fog or other hazardous weather conditions, headlights may be kept off if the driver is using their front fog lights. In such conditions, a driver must turn on either their headlights or front fog lights, or both.
Fog lights should not be confused with driving or daytime running lights, which may be located in a similar position on a vehicle, but have different uses.
For more information see the Victorian Road Safety Road Rules rule 217.