I'd say, and I might be going out on a limb :hang: but blue light is definitely good for growth. I think what remains to be seen is how plants will grow under predominantly blue verses blue and red versus full spectrum. Although with a quick search I didnt find it but I have seen graphs like above but showed the action spectrum much greater in the red range than blue, so dont take just one graph for truth. Also, many of the graphs out there just show chlorophyll a and b but dont forget there are a lot of accessory pigments which will utilize other wavelengths. If it were me and I was setting up an LED light setup I'd also at least include the same amount of red leds somewhere around 650-670nm, but thats just me. The white leds are getting better, but getting high efficient high output ones for reasonable price is still in the future I think.