While most snakes including Ball pythons spend the majority of their lives underground, they do have to come up from there hides sometimes to eat and get some exercise. I think getting a lamp just for your closet will do, it doesn't have to be a UVB or UV light it just needs to be a simple lamp hooked up to a timer to let them know when its day and night, this way the snake can go out on it's own when it wants to instead of you having to turning it on and off twice a day. As for the stress part I would think it wouldn't be a problem for your Ball pythons.

I have 4 Ball pythons ,1 Milk snake, 2 Leopard geckos and a pain in the ass Bearded dragon, and I'm constantly researching anything I can find on any and all reptiles.