In which scenario are headlights required to be on, even during daylight?

Headlights are required to be on in foggy conditions because fog significantly reduces visibility. When driving in fog, the moisture in the air scatters light, which can create a glare that makes it difficult to see both the road and other vehicles. Using headlights in fog helps improve visibility for the driver and makes the vehicle more visible to others on the road. It is particularly important to use low-beam headlights during fog as high beams can reflect off the fog, causing an even worse visibility situation.

In contrast, turning on headlights in well-lit areas, driving with high beams, or only when it’s raining does not universally meet the requirement for headlight use. Well-lit areas typically provide enough illumination for safe driving without the aid of headlights, high beams are inappropriate for most conditions including fog or in traffic due to their glare, and headlights are not solely designated for rainy conditions but for other visibility impairments as well.