When MUST you use dipped headlights during the day?

Explanation: You MUST use dipped headlights and/or fog lights in fog when visibility is seriously reduced to 100 metres (328 feet) or less.You should use dipped headlights, but NOT fog lights, when visibility is poor, such as in heavy rain.

Category: Vehicle Handling

References: The Official DVSA Guide to Driving: Section 12, Highway Code: Rule 115