In my first reef tank I kept green star polyps and mushrooms under NO lights, four tubes about 12" from the corals. They spread OK, but I was also feeding the tank a lot. I know for sure that the little bright yellow polyps (someone help me, parazoanthus?) will spread in near darkness if fed well. With a tank as deep as 36", it's going to be hard to punch light down that far. In a shallower tank, it's probably cheaper in the long run to buy a couple PCs, and you'll have a much wider selection of corals.