Fog lights in a vehicle are designed to be used under which conditions?

Fog lights are specifically designed to improve visibility during low-visibility conditions, such as fog or heavy rain. When using fog lights, the focus is on illuminating the road immediately in front of the vehicle without causing significant glare, which can happen with standard headlights in such conditions.

In fog, the light from regular headlights can reflect off the fog droplets and create a backscatter effect, reducing visibility. Fog lights are positioned lower on the vehicle and have a wide, flat beam pattern that helps illuminate the road surface directly in front of the vehicle, making it easier for the driver to see the road and any obstacles.

While heavy rain can also cause reduced visibility, it's important to note that fog lights should not be used in all bad weather conditions. For instance, using them during a snowfall may not be appropriate since the lights can create glare off the snowflakes, which could impair visibility rather than enhance it. Therefore, fog lights should be used primarily for fog and heavy rain conditions, validating why that option is the correct choice.