I keep my lights off during the day mainly because I use the sunlight/daylight. Plus, ever since my last visual flare in 2005 my eyes are ultra sensitive. I cannot tolerate bright sunlight or flourescent lighting for too long. I prefer dimly lit rooms to brightly lit ones. I guess my son has become accustomed to this because he keeps most lights off, too.
Growing up my Dad was the official "light turner offer" at our house. He had a sense of humor about it, though. He'd wander through the house declaring "this ain't the Taj Mahal.....when did I get a raise??.......nobody's in this room - guess the ghosts need the lights on.....am I the only conservative in this house??"