I'm not so sure counting lights on at any given moment is a good measure of occupancy. The resident might be at work, at the gym, out for dinner or at the cine

I'm not so sure counting lights on at any given moment is a good measure of occupancy. The resident might be at work, at the gym, out for dinner or at the cinema, at a friend's house, in another room, might have good blackout curtains and only use lamps for ambience instead of the ceiling light, on holiday. I bet if you stood outside one of these buildings where "most of the lights are off" for the entire evening, you'd see lights come on and off, and in aggregate find that most of the flats were in fact occupied. By the same logic, I could look outside my window right now, count zero cars driving down the road and declare it a useless waste that nobody uses.