Quote Originally Posted by DreadedHermie
Just FYI, you won't get very good results using "single" wavelengths (all blue for veg, all red for flower.) A rough guideline might be 2:1 red-to-blue for veg, and 8:1 red-to-blue for flower. Plants need some red even during veg for to develop mass, and some blue during flower so the plant knows whether it's day or night, and which direction "up" is (clocking / phototropism).
You are spot on about the phototropism but I'm not sure about the flowering. By using a 2:1 ratio red to blue you are esentially starving the plant's primary pigments and forcing the carotenoids to work overmuch. This prevents it from flowering earlier but also restricts the carotenoids from performing their primary function which is photochemical quenching. Flowering is a phytochrome response which is controlled by day length and red (about 660 nm) to far red (about 730 nm) ratios of light. As cannibis is a facultative short day flowering plant it will eventually flower regardless of lighting conditions. It can be kept from flowering longer than it would otherwise naturally by a) lighting it for longer than 14 continuous hours a day or b) by interrupting the night about midway by 10 min of red light. It can be induced to flower earlier than it would otherwise naturally by a) lengthening the continuous night period to 14-16 hours or b) by adding at least as much far red light as you are using red light.