They only make em as long as 48", and 4 lights in a fixture, so if you figure with VHO, you only need 2 lamps on a 72" for 320watts, the T-5 I believe largest wattage only goes to 55watts per light, you need twice as many lights to equal the output of 2 VHO lights. SOme people say they are better than VHO, but if you do the math, I don't see how they could be.