They're in range of the polar night, and headlights are mandatory to be on at all times. It can be a dark place.

Sure, but there's night everywhere at some point, it's just longer in Iceland sometimes.

During the winter, it's about 5 hours of daylight. I recommend visiting there; it's absolutely beautiful during the sunrise/set, and you'd understand what I mean about it being a dark place.

I've been, that's why I ask. It didn't seem darker than any other place at night. It's absolutely beautiful at all times, though.

I think the key fact you’re forgetting is that when it is dark in most places it is night time, which time is famous for having the fewest people driving. By contrast in the range of the polar night you could have rush-hour during what amounts to midnight in terms of ambient light. It’s really that simple.