yeah....personally, i don't turn my light on at all, the only light they get is the natural sunlight. however, when the red bellies got bigger, the light didn't bother them at all and i was able to turn it on when i wanted to view them at night without an issue. My tiny 3 inch rhom doesn't mind the light at all. He tends to notice his reflection and come out to the glass when the light comes on. I Guess you're just going to have to make a decision, force him to get use to the light or go without.
i do want to point out i'm comparing red bellies to your elong though, and so is the guy above. elongs are faster then red bellies and ambush predators that attack using surprise and speed. in other words, they'd be better built for catching tetras