You don't need moonlights, it's more for your own amusement then for the tanks benefit.
I had lights on my tank right from the beginning, just so i could see all the stuff on the rock but some people will probably say it's better to cycle the tank without lights.
Once fish are in the tank they will probably prefer some kind of light during the day (just so they know when to go to bed
)
and last, I try to keep some kind of lights on for 12hrs a day just because the daylength is fairly constant at the equator where most of our tropical stuff comes from.