<a href=showthread.php?s=&postid=9740177#post9740177 target=_blank>Originally posted</a> by hahnmeister
LED is able to focus its light into the tightest, narrowest, almost laser-like focus of output. So that LED may not make much light, but what it does make, it is able to concentrate so well.
This comes at a price though. You may be able to light your 150g with one if the dimensions are 72x18x30"high, but not if its 72"x30"x18" high, because the LEDs wont cover the 30" front-to back of the tank. They are like little spotlights, so even people who try to grow corals on the back wall of their tank are having trouble, because the light drop-off is very severe when you move out from directly under the LEDs.
So the solution may be to use lenses to help spread out the light source across a wider area... well... when you widen that 15degree cone of light to 30degrees, you just cut the intensity by what... 4x, or 8x... and then LEDs have lost their advantage as well.