I have a 29 gallon biocube. I have mushrooms, xenia, yellow leather, torch, duncans, green star poylps. I use the stock lighting that it came with and have had no problem. I have seen good growth on everything (except the duncans just added them this week). It has two 36 watt power compact bulbs...that is 72 watts of light for 29 gallons. If you have 3-5 watts of light per gallon you should be fine. So the initial posting of 20" Orbit 2*40W SunPaq PC Fixture w/Lunar Light and Fan would be more than fine. If you have $250 to spend though, I would think about just getting into a biocube or something like that. If you get something that needs more light you may have to place it closer to the top of the tank. Just my opinion.