I'll give you a specific example, this is a question I personally posed to the enforcement division years ago.
At the time I had a fiber optic sight on my bow, that used a small, external led mounted sideways, projecting light into the sight, not toward the animal. It was a removable device. I asked about it's legality and showed it to the game wardens I was teaching with that day. They both agreed no issue because it illuminated the sight and not the animal.