When Headlights should be switched on by law?

Headlights must be switched on by law during low visibility conditions, such as fog, heavy rain, or snow, where the driver cannot see at least 100 meters ahead. They are also required to be used from sunset to sunrise and in tunnels or other enclosed spaces. Additionally, some jurisdictions mandate headlights to be on whenever windshield wipers are in use. Always check local regulations for specific requirements.