I don't remember who it was but years ago someone told me that they put the miniature Christmas lights in their coops all along the perches. They had modern game bantams and these little birds found out that these little lights gave off a little heat. The person said that the birds would position themselves over a light when they went to roost. Pretty interesting. I would likely use the regular large bulbs (4 watts) but then there's that electrical problem too and would the birds peck the bulbs? Probably. If there were possibly Christmas lights that would plug into a cigarette lighter and run directly off the battery, I don't know if it would make any difference or not, it's still electrical.
Isn't the problem with electricity related directly to mice and their chewing "disorder?" If you ran electric wiring through metal conduit pipes, that would eliminate the mouse side of the problem.