Nobody said it would keep corals from spawning or of the sort. I thinner the arrivals are more towards the natural feel for the inhabitants and also the night dwelling guys come to life a bit more.its been awhile since j read any arrivals but if a fish is pulled from the ocean and stuck in a tank I would think that it would be a worsened experience to just all the sudden be blacked out at night. Corals could probably care less but the fish and inverts are what use that lunar lighting even though mine peak at 470nm