When should headlights be used?

Headlights should be used whenever visibility is reduced to ensure safety on the road. This includes conditions like rain, fog, snow, or any other time when natural light is insufficient for the driver to see or be seen by others. Using headlights in these situations not only improves the driver's visibility of the road and surroundings but also makes the vehicle more visible to other drivers, helping to prevent accidents.

In contrast, the other options imply limited use of headlights. For instance, using them only after sunset or just in residential areas ignores the necessity for safety in varied driving conditions throughout the day. Limiting headlights to nighttime would also be unsafe during adverse weather or other low-light situations when visibility is compromised, regardless of the time of day. Therefore, the best practice is to utilize headlights whenever visibility is reduced.