I have an AquaticLife 36" T5HO with one 6500k bulb and one Roseate bulb, I'm using 3 layers of the gray screen over my 12g Long. I'm only using the stock legs that came with the light to elevate it above the tank, so at it's highest point, the light is about 14" above the substrate, and at the lowest, about 8".
The tank has only been filled for one week, but so far so good. I'm debating on removing one layer of the screen. My photoperiod is 6.5 hours right now.