After over a year researching what I was going to do with my DIY fixture here's what I came up with that anyone thinking of doing something like this needs to keep in mind:
1) Corals typically grow under natural sunlight which has an extremely vast range of light wavelength - the range of those wavelengths gets shorter and shorter the deeper you go.
2) I believe, that the light we create needs to re-create that spectrum as close as possible to achieve as natural as possible coral growth.
3) LED's light spectrum's are incredibly narrow. So the more variety you have the closer our light fixtures reach natural light. I personally have issues with fixtures that only have Royal Blue and Cool White LED's. Sure they will grow stuff, and sure they look ok to the human eye. But I sincerely believe that they lack 90% of the spectrum (or more). And we really have no idea exactly what parts of the spectrum every symbiotic algae needs in the corals, clams and other creatures that may live in our tanks. It is my personal opinion that is why MH lights work so well over 99% of LED fixtures. They provide the entire light spectrum while every single LED fixture produced, does not.
4) You can cut out certain wavelengths (and this may indeed be desirable in some cases) as some wavelengths do seem to grow undesirable algae's better than others.
The whole subject is difficult to grasp and is not fully understood by even the leading scientists. But it only seems logical that we need to recreate as close as possible natural conditions within our personal constraints of fixture size, budget etc.
And, yes, I know that my ramblings may not be entirely helpful, lol
