In weather conditions that significantly reduce visibility...

All vehicles travelling between sunset and sunrise, or at any time of day in tunnels, underpasses and road sections affected by the 'tunnel' sign, or at any time of day when meteorological or environmental conditions significantly reduce visibility, must have the appropriate lighting switched on. In the case of particularly adverse meteorological or environmental conditions, the rear fog light shall be used together with the sidelights and, in addition, the dipped headlights, the high-beam headlights, or the front fog lights. We must never use only the rear fog light, as indicated by incorrect answer b).