When should you use fog lights?

Answer: C — In dense fog with visibility less than 100 meters

Using fog lights is specifically intended for situations where visibility is severely reduced due to weather conditions, particularly in dense fog. When visibility is less than 100 meters, standard headlights can create glare and reduce visibility further, reflecting off the fog or mist. Fog lights are designed to emit a wide, low beam that helps illuminate the road directly in front of the vehicle without reflecting back, enhancing forward visibility in such conditions. In contrast, using fog lights in clear visibility conditions or during heavy rain is not advisable, as they can cause glare for other drivers and are unnecessary. Fog lights are also not meant for general nighttime driving when it is simply dark outside, as standard headlights are sufficient in those situations. Thus, the appropriate usage is clearly defined for conditions of dense fog, ensuring safety for both the driver and others on the road.