I have went complete LED on all tanks and gave had excellent results. If you buy a pre made fixture, a lot is going to depend on the old saying, "You get what you pay for."
My SPS grows very well under the LEDs in my 180. They were under 250 watt 10K XM halides being pushed by Ice Cap Ballasts previously. XM is one of your better PAR bulbs and is known fir good growth and I'm getting the same rate switching to LEDs without the gross yellow ting of the dreaded 10K bulb.
I like that (if you have a dimmer) you can change the color range to your liking without sacrificing your PAR. My local reef club has a PAR meter that they lend out and we found that regardless of whether the whites were ran at 50%,75%, or 100%, the PAR didn't change. So now my tank has the look of a 14K with the growth of 10K.
You still get the shimmer, if not more so than you do with halides. No heat! I actually have the opposite issue now, I have trouble keeping the tank warm enough, but adding a heater is a lot cheaper than running an extra AC just for the fish room and a chiller.
I'm able to keep my macros alive in my seahorse tank as well as not having to run a chiller for them.
Since switching our 180 to LED, we saw a $75 initial drop in the electric bill monthly. I then added other tanks, so I can't give any more accurate info than that.
I was very skeptical of LEDs as some were complaining of color loss, especially on their SPS, but I haven't seen this. In fact, more colors pop now.
The next issue of Coral Magazine (Sept/Oct) is devoted to LEDs and other new light technology, if you can hold out until that issue comes out, it might really be to your benefit.
