I've been wanting to set up a show fuge next to one of my reef tanks, but I can't come up with a way to keep the fuge lighting from affecting the reef tank. (Without looking really ugly, anyway.)

But that started me wondering how much effect the other house lights have on my corals at night. I have one tank that is relatively near a hallway light that my daughter likes to leave on at night. We also leave a kitchen light on most nights. And even though it is not very bright in the next room where the other tanks are, it is still far from night-time darkness. Some mornings I notice that some of my tank inhabitants don't seem to have closed up at all overnight.

So the questions are these: just how detrimental is background house lighting to a reef tank at night? Is it necessary, or better, to have a period of total or near-total darkness?