When the weather closes in, two things matter: how well you can see, and how well others can see you. Your lights do both jobs, and using the right ones at the right time is a genuine safety skill, not just a switch you flick.
In dull, rainy daytime gloom, dipped headlights make you far easier to spot — even though you can see fine yourself. The point often isn't your vision; it's being visible to everyone else.
Fog lights are the bright extra lamps for thick fog. The rule that catches people out: only use them when visibility drops below 100 metres, and switch them off the moment it lifts — in clear conditions they dazzle the drivers behind you.
The bits that matter
- Use dipped headlights in gloom and rain so others can see you.
- Fog lights only when you can see less than 100 metres — off as soon as it clears.
- Don't use full beam in fog; it reflects back and makes seeing worse.
Memory anchor
Fog lights on under 100, off the moment it lifts
Picture 100 metres as a football pitch. If you can't see across one, fog lights go on. The second you can see further than that, they go straight off — they're a tool for thick fog, not a style choice.
Out on the road
The motorway fog bank
You hit thick fog and switch your fog lights on. A mile later it clears to bright sun, but you forget to switch them off — and the driver behind is now squinting into two dazzling red lamps, unable to tell if you're braking. Off the moment it lifts: that's the courtesy and the rule.
The mistake everyone makes
Full beam in fog
It feels like more light should help, so people flick to full beam in fog. It does the opposite — the beam bounces off the water droplets straight back into your eyes. Dipped beam, plus fog lights if it's really thick, is what actually lets you see.