1 gallon won't hurt them. I never use lights. Some people leave lights on all day and all that comes of it is algae on everything. I hate that. How many fish live less than a foot away from the sun? None. So they shouldn't live directly under a light that is on 12 hours a day. As long as they are in a room with a window or where people have the room light on sometime then that is enough light for the fish.