well, i think there is more to it than that. i have noticed that some LED
fixtures lack the spread, so even if you have 24 of them, you might have visible gaps. plus there are optics to think about. these channel the light a bit, and will effect the intensity.
also, dimming- if you can't dim them, they better have the correct mixture of white and blue, otherwise the corals may grow, but they colors won't pop.
then heat reduction- some have heat sinks, some have fans, some have both. what is necessary?