I think the best way to go about the lighting issue is to break it up a bit.
High light - light loving animals throughout the tank, from the top of the tank to the bottom, clams on the bottom of the tank.
Medium light - Light loving animals at the top of the tank, lower light required species at the bottom.
Low light - Really, a softy tank. Maybe a few montis or LPS up top, and very low light animals at the bottom of the tank.
High light--
18 inch deep tank or less 150 HQI/175 MH plus supplemental lights per 2 square feet.
24 inch deep tank or less 250 W MH plus supp. lights per 2 square feet.
more than 24 inches 400W or greater per 2 square feet.
If using T-5's, as many T-5's lights as will fit across the tank (Probably need 8 T-5's spanning the full tank)
Medium Light --
18 - VHO/PC @ minimum of 6W per gallon or 70w MH/poor PAR 150/175, no supp.
24 - 150/175W MH or approx. 4 T-5's spanning the tank
>24 - 250W MH or approx 6 T-5's spanning tank
Low light --
18 - normal output Fluorescents over tank (ie 4 40W fluo. over 55 gallon tank)
24 - VHO/PC's no more than 3 or 4 watts per gallon (4 65W PC's over 90 gallon tank)
>24 - same as 24 inch tank above.
HTH. And feel free to flame me on any of the above statements. I know that there are exceptions, and I am more than happy to hear about them.
