+1. LEDs have a big flexibility advantage that's completely absent in other forms of lighting - we can swap optics to change where the light goes. With T5 or MH, you typically have only a few reasonable reflector choices, and little or no control over "spread."
Meanwhile, with LEDs, you can put the same array on a 12" tank or a 30" tank and get the same PAR at the sandbed by swapping optics - as long as you understand the increased intensity on the taller tank with narrower optics comes at the cost of decreased spread.
Search this forum for widmer's projector thread - he mounted an LED array on his ceiling and there's pretty much zero spill outside his tank. More or less impossible with what we have available for other forms of lighting, and the same technique could be used to get incredible PAR all the way to the sandbed of the deepest tank you could fit in your home.
this is something people have a hard time understanding. An optic is something that is used to focus the beam kind of like a mag light. you can make it as bright and pin point as you want or as flooded as you want. this is what is great about LEDS. when I was runing my LED diy system I only cleaned the glass maybe once every 3 weeks. this is because the light is shooting straight down and not on the glass.
der_wille_zur_macht - thank you for the links.