Wow, this turned from a tank shot page to a Why LED page quick :P
My 2 cents. Cost isn't going to be huge saving, like people have said and showed, cost of builds and electricity savings are going to eventually pay off the LEDS. But as also stated, people are assuming the LED's and drivers won't malfunction during that time (technically they shouldn't... but...). Same goes with MH too though, as i'm sure anybody using an old humming ballast knows.
The HUGE benifit in my opinion is the wave length on LED's... it doesn't change. No color shifting after 6 months like MH(even the best bulb will have some shift.) The output is at least 70% after 5 years of 12 hours a day use. Most people are underdriving their DIY systems, so they can increase to get that 70% back later on. Big setups are usually driven to max, but have sufficient cooling so that it won't matter.
People ahave been arguing the PAR rating etc, but PAR is a poor measure of what we need, most meters check all light between 400nm-700nm and give back the average over that amount. What we really need is the used wavelengthss since coral doesn't use an average from 400nm-700nm. PUR is better, but hard to measure. What you CAN see is the output of LED's on a wavelenth compared to what algee needs to grow. This is why i'm going LED's(not cree LED's or a good MH bulb/balast, but you can find wavelengths for both from cree's site and from sanjay's site, just a good general example)
http://aquariumdigest.files.wordpres...mh-4.jpg?w=500
Here's some links on LED's that should relate to this "tank pics":
benfits:
http://www.nano-reef.com/forums/inde...owtopic=186982
Tank Pics(nano's but shows):
http://www.nano-reef.com/forums/inde...owtopic=200335
LED build with par readings(my favorite LED tank so far):
http://www.reefcentral.com/forums/sh....php?t=1761942
http://www.reefcentral.com/forums/sh...&postcount=388 (vid's)
Here's a pic of that tank:
http://i45.tinypic.com/ibkvth.jpg