Mike,
I need a 60" light for a planted freshwater tank, so I need a lot of light. a singe fluorescent would not cut it but several would do the trick. The tank is 125g and the rule of thumb as I far as I know is about 2-3 Watts per gallon. MH will burn the plants, but any type of fluorescent should be just fine.
Do you have something in mind?
John