if you consider a metal halide bulb to be about 1.5" in diameter and say 5" long and a t12 to be 1.5" in diameter.... the metal halide bulb's 9 bend reflector is around 12" by 10" by 5" high... you couldn't even put two VHO
light bulbs on a 55 gal
tank (assuming reflector being 48"x10"x5" high)but the T5HO is only 5/8" in diameter and its reflector is only about 2" wide...T5HO=54watts-5000lumens-20000hrs life and VHO
even if you don't use any reflector or just the "standard" reflector you would use the same number of bulbs at half the watts and twice the life.
I make digital ocean maps for a living and do not sell anything. I just did my research on tank lights about a month ago and totally talked myself into T5's, BTW
I haven't bought then yet because two light retro kit costs about 130 and two bulbs about 50 so I need 180 bucks per set.