techniqually you can have lunar lights.... or would u liek to be in the dark all the time?... most fish you get arent while and are tank bred and are also use to our hours
its very cruel to not give your fish night time/day time hours especially if you have nocturnal fish.Some of my nocturnal fish will go about their business under a moon light but not all.My BGK will only come out once all lights are off.
Keeping lights on 24/7 is actually a form of soft torture,one which often leads to odd behavior from your fish after some time,anywhere from strange to downright spastic.
I guess some people use the tank as a nightlight or something I don't understand what other reasons there are for leaving the tank light on while your sleeping.