When can the rear fog light be used?

What does this rule or driving tip mean? A rear fog light is very bright. It helps in extremely poor visibility, but it can dazzle drivers behind you if it is left on unnecessarily. How to use this safely Use kilometer markers to estimate fifty meters. Also adjust your speed and following distance. Switch the light off as soon as visibility improves. Driving lesson and exam tip Know where the switch and indicator light are. In bad weather, you want to be able to operate it without having to search for it. Remember: use the rear fog light only in fog or snow and when visibility is below fifty meters; switch it off again afterward. View the source: RVV 1990, article 34.