I have a DIY moonlight over my tank. It is a blue rope light that I've attached to the top of my canopy. The results are every bit as effective as the "official" moonlights, and it cost me only 6$, instead of around $100. Essentially, all of these put a dim blue light into your tank during the night, allowing you to see your animals, but not enough light to disturb them. Another solution some have done is placing a clip on desk lamp on the back of the tank and putting in a little blue bulb, or putting a blue (or red) film over the front so it isn't as bright. Anyway, this has been talked about before. If you do a search for a thread called, "anyone know about a moonlight?" you'll see my more detailed explanation of the rope lights, including pictures.