How do you sleep – with or without lights on?

I was talking to someone recently and a something which they said really got me thinking. They said that they simply cannot sleep with the lights on. So I am wondering….how do you sleep…with the lights on or off? I am not one of those people who can sleep with the lights on, unless of course I am totally exhausted. In this case I fall asleep as soon my head hits the pillow. But it seems that some people love sleeping with the lights on. They simply dislike total darkness. Sure I keep a light on in the main corridor or maybe the staircase just in case someone needs to go to the fridge to get something or go to the bathroom in the middle of the night. But I simply cannot have a light on in the room where I am sleeping, because even with my eyes closed I will still see a lot of light. If I am sleeping at someone else’s place, and they are sleeping with the light on….then I usually cover my eyes with some cloth so that the light doesn’t disturb my sleep.