Thought I'd comment on the growth question upthread
I set my 120 up with LEDs and only put frags in it. I recently added 12 more LED but for most of the first year I was running 84 LED over a 4x2x2 foot 120 tank, 3 watt crees, no otics running at 750ma. My rocks go a little over halfway up the tank. I have a green Monti Cap that has gone from the size of a silver dollar to about the size of a saucer in about 1 year. I have a meteor shower cyphestra 9sp?) that in about 9 months has spread down the sides of the original frag and across the plug it's mounted to. A Monti Digitalia that started as a stick is the most telling. It has spread across the top of the rock with very little vertical growth. It's obvious it's getting plenty of light because it's not reaching. I have a rose bubble tip anemone I haven't fed in months. It hangs out about half way up a rock at the end of the tank a few inches beyond where the LED's stop.
My LED's were built to be moderate light. I have 6 rows running the length of the tank spaced out about 2 3/4 inches apart except where a added additional LED's a couple months ago. That ain't diddlysquat compared to what a lot of people use. I run a lot of Royal Blues in my mix, nearly 3 to 1. A PAR meter doesn't read blue light very well and the deeper into the blue spectrum you go the worse it reads. Apogee who makes the meters has said they estimate a 20% under read of blue light. I personally think thats a very conservative estimate but I get PAR readings in the bottom of my tank in the 120's. Even taking that as an accurate number it's enough for SPS as long as they are a decent way up the rocks.
Using 3 watt Cree LED's I wouldn't hesitate to grow SPS in a 36" tall tank using the correct number of LED's and the right optics. With some of the new Cree chips that are out now I believe you could use LED's in place of 1000 Watt halides once the right colors are available.
