I have had LED's over my DT since my current tank-build, late 2011.....I 've never had MH lighting so I can't personally comment or share my experience about them. What I can say is that I purchased my LED lighting in late 2010 and they are currently antiquated as far as color spectrum. When I purchased my fixtures they had all the bells and whistles (some of which I quickly grew tired of...IE: thunderstorms and moving clouds to a lesser amount), however I still love the control regarding color and intensity. The real issue with my antiquated fixtures is that they only have 3 colors: cool white, blue and royal blue. I have 3x180 watt fixtures with the whites running @ 35%, and the blue/royal blue running @ 85%. I could sustain SPS corals but the growth rate was tremendously slow. In the advent of all these other colors being added (deep red 660nm, cyan 500nm, violets 400 to 420nm, different arrays of white etc), I felt that my lights were deficient regarding total broad spectrum. Rather than sell my lights (I originally paid $2500 for them) for a
huge loss, (I was offered $600 for all 3 LOL)....I chose to supplement them with 2 sets of 2 x 80 watt T-5 retrofit kits. I added a midday sun, aquablue plus, true actinic 03 and purple plus.....I added them about 4 months ago and there has been a trenmendous difference in growth, (but not coloration which was good to begin with). NOW....I am not attributing this growth to simply the addition/use of T5's but rather to increasing the color spectrum....however ....of course I can be wrong, (it wouldn't be the first or last time). My 3 fixtures alone...never gave off a spot light or shadowing effect...at least not that I noticed....THESE FIXTURES HAVE
NO optics so maybe that's the reason. Alot of the comments I have read in this thread may be attributable to the use of 60/80/90 degree optics...couple that with the height/placement above the water and YES there may indeed be shadowing or possibly attributable to a deficiency related to the number of fixtures utilized. Regarding electric usage I AGREE 100% that there may not be the advantage that was once thought regarding using LEDs....In my case ....3 LED fixtures x 180watts = 540 watts plus 4 x 80watt T5's = 320 watts for a total of 860watts....(althought technically I am NOT running the LEDs at full intensity) versus 3 x 250 watt halides = 750 watts. However, I do not need or use a chiller which I definitely would need with the halides...so I guess you save that electricity cost. There are a ton of LED manufacturers out there today and the prices have come down a bit, (significantly on some fixtures, {ocean revive, IT2040's Evergrow D120's etc}...while others still would put you in the $2000 to $3000 range for startup costs). That being said I still think the technology is evolving....and the color spectrum needs to be ironed out. Pacific Sun has fixtures where NO white LEDs are utilized yet they claim to cover the entire needed color spectrum. Did anybody ever take a look at some of Sanjay Joshi's articles on LED's and comparisons with MH/T5 lighting? See here:
http://www.advancedaquarist.com/2010/2/aafeature2
Keep in mind this article is old, (2010), there are many subsequent articles.
I do agree that perhaps more LED fixtures may be warranted for proper spread than prescribed by the manufacturers, (dependent upon the fixture/height/optics utilized), however not a preposterous amount that would virtually cover the entire top surface of the tank.
Many factors dictate success in this hobby inclusive of water quality, flow and PERSONAL PREFERENCE ......I belive LED technology will keep getting better...unfortunately the prices of the higher end fixtures have not reflected that just yet......for now I will stick with my 3 antiquated fixtures and supplemental T5's.........of course these are just my opinions.