When the visibility is down to less than a couple of hundred metre because it’s snowing people don’t put their lights on? Seems to be grey cars in particular, obviously not a scientific survey.
Really annoys me.
Rant over, oh, why do student cyclists in sheffield think they are luminous? The number riding through Crookes and walkley without lights really annoys me too.
Properly over now.

If you have to use your windscreen wipers (in daylight hours) then switch yer bleedin lights on. Simple rule. Easy to follow.