Moonlighting would not be a thing fish need as far as I can tell. Its a relatively new thing in the hobby and the one effect on fish health I can think of might be let them get less sleep/rest if it were left on all night and their natural instincts were to be used to periods of deep darkness. I assume moonlighting itself is something completely dreamed up for people, just like shipwreck decorations.
Normal artificial light, like we commonly do with fluorescent tubes and perhaps timers is something that deserves a good deal more attention before one might declare it bad or good. Have you ever thought about whether our artifical lights make our fishes environment seem strange and alien or normal and comfortable from their viewpoint (not to project the idea that fish have "viewpoints!" but you get my meaning)? The problem is that fish came, at least in the past before being bred a lot in captivity, from all sorts of different habitats, usually depending on species. Their habitat might have been it deeper, darker water or it might have been in sections of brightly sunlit river or streams, or they might have been in lakes where they themselves could make a big difference in light depending on where they swam.
Even for humans, light in the environment is complicated, providing Vitamin D and yet also being a danger for skin cancer. Then there is the whole thing of seasonal psychological problems for humans who don't get enough light. Or conversely, the problems that might be associate with not having a dark enough environment during sleep, there are studies about that too I believe. So I think the subject of light with respect to fish is just another of those areas that, while we can be confident that we are not doing things that are too terribly wrong, is still an area where we humans/hobbyists should be humble enough to admit that probably we are probably pretty deficient in the overall completeness of our knowledge, or the application of what science we do know.
~~waterdrop~~ (sorry, can be dangerous to catch waterdrop in the middle of the morning cup of coffee

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