The 36w reflectors from AH, if I'm not mistaken, are 22" and the bulb is 18". So how do you think that would compare with a 24" 24w T5HO with a 24" reflector?
The bulbs are 16.5 inches long. As I said above, you would get about 70% of the PAR that a single T5HO bulb would give, and the T5HO would be 24 inches long, so it would cover the whole substrate better. I use one of the 36 watt AHS kits over a 15H tank, which is 20 inches long. I get about 30 micromols of PAR with the light 23 inches from the substrate, and it is uniform over the entire substrate. If the light were 16 inches from the substrate I would get about 70 micromols. If the tank were 24 inches long, the intensity might drop a little at the ends of the tank, but not by much, with the light 23 inches high. It would drop more with it at 16 inches, however, if you keep the inside and outside of the glass sides and ends of the tank very clean, you get much better uniformity because of reflection off the glass.