An observation on lights

[JMurphy97]

Why is that for a 48" tank you can get light like this and be fine:

http://www.thatpetplace.com/maristar-hqi-t5-combo-fixture-48in

It uses 2 250w halide bulbs and 2 54w T5 bulbs.

But if you choose to go LED (most popular are AI abd Ecotech) you get people saying you need to have 3-4 units? My understanding is that the
250w halide bulbs give you a coverage of about 24" by 24", or 2 feet. Is not one AI able to cover a 24" by 24" area if not mounted parallel to the front
(--) and dividing the 24" in half and in the middle of the tank? It's hard to explain without drawing it out and whatnot. Does anyone else see my point or am I wrong?

 

[Playa-1]

I believe it has to do with par reading and usable light on the outter edges of that 24x24 area. There is a whole lot that goes into the planning of the lighting systems and that is why so many people opt for a DIY build as opposed to a prepackaged LED system. Things such as aquascaping could play a huge role in what will and what will not work for you.