Front fog lights are of use in extremely poor visibility. In this situation, the normal low-beam lights reflect off the fog in front.

Fog lamps are intended to provide an adjunct to the low beams. Because fog hovers close to the ground, the lamps are designed to shine down, illuminating the road beneath the fog. 

The top of the beam is cut off sharply so the light does not shine into the fog and reflect off it.

Front fog lights are mounted low down on the bodywork, and are angled down at a steeper angle than normal headlights. 

The beam pattern is wide and flat, with a distinct cutoff at the top-this reduces the amount of light reflecting off the fog. 

By switching the low-beam lights off, the driver can use the fog lights to illuminate the road directly in front of them, so they can proceed at low speed.