I've got a 42g and 55g both of which are same depth, a 250w HQI over the 42 and 4 x 54w T5's on the 55g, to give ya an idea of depth penetration I'm seeing, my green button polyps in the 55g (on the sandbed) are nice and big, great coloration, and very short stalks, a fragged colony of the same polyps in the 42g (on the sandbed as well) are reaching with all they have for light, coloration is a tad off but still looks good. I definatly have to take care with the hieght on my T5 fixture as it tends to burn the corals when too close (I have to keep the fixture higher than I keep the MH fixture over the other tank). But my 250w is also a cheapy brand, may make a difference in intensity and all.