The blue LED "lunar lights" are basically just for your benefit in order to view your fish at night. Many fish and inverts are nocturnal, so it gives you the ability to see them when they are more active. I've heard it mentioned it can trigger breeding in certain species...but I'm not sure if there's any truth or if that's just rumor. There are other lights like actinic which are blue, but they should not be left on all night. The lunar lights would be fine, but I still turn mine off at bedtime.