Under what condition are fog lights legally required?

Fog lights are legally required during periods of limited visibility, such as in fog, heavy rain, or snow. This is because fog lights are specifically designed to illuminate the road directly in front of a vehicle at low levels of brightness, which helps reduce glare and improve visibility without reflecting excessive light off the fog or precipitation. When conditions such as fog create a reduced visibility environment, using fog lights becomes essential to enhance safety on the road by allowing the driver to see and be seen clearly.

The other options do not align with the law regarding the use of fog lights. For example, using fog lights on sunny days or in heavy traffic does not address their primary purpose, which is to improve safety in limited visibility conditions. Additionally, fog lights should not be used in conjunction with high beam headlights, as high beams can create too much glare in fog or heavy precipitation, making it harder to see rather than easier.