It's weird, one of my sons sleeps with the light on every night at home, 8 yrs old. However sleeps happily in his swag. I was surprised to be honest. A couple of things that I do.
Make sure he has his head torch in there and it's working, show him how to keep it in the same pocket.
Always put the zips in the same place.
He had a few nights in it in his bedroom, opened up when he first got it.
Let him bring a couple of teddies with him.
Use the same pillow he has at home.
He also has his iPod in there with him.
No problems at all. In fact it's the one place he tends to sleep in !