To add to that, here are some typical °K and nm values I'd been seeing for LED's. (To convert back and forth between K and nm, divide 3,000,000 by the figure, apparently).
Cool White 8000°K (as well as 5500K-10,000K)
Pure White 6000°K (also known as xenon white)
Neutral White 4200°K
Nature White 4000°K
Warm White 3000-3300°K
Red: 625-660 nm.
Green: 525 nm
Aqua: 505 nm
Blue 470 nm.
Pink 440 nm.
Violet 420 nm.
Ultraviolet LED's range from 380 nm to 405 nm.
Thus, to cover the spectrum at 405, 440, 640, and 620 for both chlorophyll A and B and thus to best suit your plants, you could use Red, Pink, and Ultraviolet LED's?
The low end of both warm white and even cool white still seem to be a bit to high for optimal plant growth. So it would still seem best to supplement white LED's with some ultraviolet LED's?
I'm not sure what that would do to your color rendition, but warm and cool LED's suffer a big drop in the 500 nm region of light, which could be supplemented with some aqua and some green. (That might not make your plants grow any better obviously, but might nevertheless help your color rendition).
I'd also bought an RGB LED strip to play with, but unfortunately it doesn't fit within the very tight slots I have for LED strips in my hood as it's a little wider.
And yes, these are your standard LED's that I'm talking about here. I wouldn't doubt that some more expensive ones such as CREE's perhaps might have better color rendition and PAR over the spectrum that plants use, but those are not the LED's that I'm asking about just now.