Full spectrum is basically entirely for coloration.
Advanced aquarist has a good review on fluorescence, and fluorescent pigments in corals. This has been thoroughly discussed in scientific literature (and continues to be discussed). (
http://www.advancedaquarist.com/2006/9/aafeature) If you guys take a look at figure 2, it highlights the broad spectrum of wavelengths (both visible and UV) that fluorescent pigments in coral cover--the more of them we hit with our light's emission, the more vibrant our corals look.
In terms of growth, there are photosynthetic pigments that absorb into the visible as well (and even approaching the near IR... or well into the red), but the most common ones (the chlorophylls) absorb around the wavelengths that 'blue' and 'white' LEDs emit.
http://reefbuilders.com/2010/08/23/c...nfrared-light/
The reason people switch back to T5 and MH light sources is because these lamps are broadband emission sources, so you're hitting both the growth wavelengths and the other visible wavelengths all with one lamp, resulting in growth AND pretty colors. LEDs are narrow band emitters (ie: they just hit specific bands), so including different colors of LED
helps with color rendition. LEDs have other advantages; smaller fixtures, run cooler, use less power, long bulb lifetime, etc.
As a guy who works on LEDs on the molecular level, I'm stoked about the technology. Sure there's room to grow, but people hanging onto MH and T5 systems may be a little afraid of change.
