I started sitting for others at 11... and by 13 was sitting at least 2 nights a week almost every week (rotating between 3 or 4 families on a regular basis). By 14 I was working a "real" job that paid by the hour 4x what I made sitting. I not only then, but also at 31 leave all the lights on, especially in other people's houses.
In the dark in our own house, it's not easy to trip, but in other people's houses... crash. Your kids were great, sorry I broke the urn with great aunt Lilly... not a good night. There's also the fact that lightswitches are in weird places in other people's houses. And (with curtains drawn) it makes the house appear occupied by awake people (something taught in Red Cross Baby sitting classes is to leave lights on in various places in the house to discourage burglers). And on top of all the rest... it just feels safer / happier/ cozier. My husband gets ticked off at me that I leave the lights on in the house at night... but I WORK at night. I'm up... moving from room to room (bathroom, kiddo's room, let the dog out, grab a snack, let the dog in, work, bathroom, dog, laundry). I don't want to live in a cave. I can throw open all the drapes in the daytime and not be in the dark... but not so at night. At night, I need the lights on. The extra $11 a month is just plain worth it to me 1000x over. ((I was gone for a month so I based the added electric bill off of that month)). And when my husband goes into the office or the studio at night he turns THOSE lights on. Because he's working. So I think same should go for myself. (I also leave lights on when I leave the house, but that's because I've been attacked in the dark before and I will NOT willing come home to a dark house unless I'm armed).
So... personally... if the only two things are bothering you are the lights on, and not checking to make sure blankets haven't been kicked off... I'd keep him. I'd let the lights slide (after all he's "working" at night while you're gone), but just give him a heads up that one of the boys kicks his blankets off.
I WOULD however, put a "minimum" age limit out there. Tell the 11yo that when HE'S 13 (or whatever age you feel comy with) he can babysit also.