Ross,
"T5 fluorescent bulbs are simply 5/8” diameter fluorescent tubes. (A standard output fluorescent or VHO bulb measures 1-1/2” in diameter.) It’s this slim profile that makes T5’s much more efficient than other types of fluorescent lighting. In fact, on a watt per watt basis they put out more light per X amount of energy consumed than standard fluorescents, VHO’s or powercompacts. Also as a result of their slime profile it is much easier to create a highly effective parabolic reflector that directs more light down on the tank than reflectors for oddly shaped powercompacts or bulky T12’s. Normally driven T5 bulbs also last longer than VHO’s or powercompacts."
30 L aquarium, 50 lbs LR, 44 lbs LS, 192 W PC, CPR Backpack Skimmer