During what situation is it necessary to turn on vehicle headlights?

Turning on vehicle headlights is essential when visibility is low due to weather conditions or darkness. This includes situations such as driving in rain, fog, snow, or during dusk and dawn when natural light is insufficient to see clearly. Headlights help illuminate the road ahead and make the vehicle more visible to other drivers, reducing the risk of accidents.

In contrast, while there may be circumstances where headlights could be on during bright daylight, they are not a requirement, thus making those situations less critical than in circumstances of reduced visibility. Using headlights only at night does not encompass all scenarios where visibility can become a concern. Additionally, when parked on the side of the road, headlights may not be necessary unless specified by local regulations, but they can improve visibility for the parked vehicle's safety.