Your Headlights Are Your Speed Limit

The handbook states it directly: do not over-drive your headlights — do not go so fast that your stopping distance is farther than you can see with them. It adds the reason in the same breath: give yourself enough room to make a safe stop.

Make it arithmetic, as Vision & Perception did. At 100 km/h your dry stopping distance is around 92 m. Dipped beams light roughly 50 m of road. Drive at 100 km/h on dipped beams and you are committed to 42 metres of road you cannot see — and anything within it that isn't moving out of your way is already unavoidable when it appears.

This inverts how most drivers think about night speed. The speed limit is a legal ceiling, not a safety figure — at night the binding constraint is your light. On dipped beams, safe speed is markedly lower than the limit. On main beam you see further and may go faster, which is exactly why the dipping rules in the next sub-topic cost you speed as well as vision.

And there's a trap the handbook names specifically: reflective roads mislead you into believing you can see further than you really can. A wet or polished surface throws light back, and the road looks lit well ahead — but what you're seeing is the surface reflecting, not the objects on it. A dark-clothed pedestrian or an animal standing on a shiny road is invisible until far closer than the apparent visibility suggests. The road being visible is not the same as hazards on it being visible, and this is the specific illusion that produces night collisions on wet tarmac.