Quote Originally Posted by thepaan
Are you growing space-weed? What does the solar radiation at the edge of the atmosphere have to do with anything? I don't think the relative intensities of different wavelengths of sunlight have anything to do with it either. As green and yellow are also more dominant wavelengths than red, your logic suggests you should add lots of those to your LED array. Let me know how that works out.
I'm very confused as to how you managed to infer what you just stated from my post.

Where is this stuff saying blue light is better for driving photosynthesis?
http://www.emc.maricopa.edu/faculty/...BK/pigment.gif - something from an educational facility. http://3.bp.blogspot.com/_pFQ0wrHWd1...pectrum_en.jpg - there's another.

All the studies I've read say that photosynthesis only occurs at around 50% peak rate on blue light alone
Depends on the plant being studied - not every plant responds the same - every species has vastly different requirements. For example Tradescantia pallida actually thrives under yellow and green light, which is why it does so well on the forest floor and in well-shaded areas. If you have the materials to conduct a colorimetric analysis, you will see that against a blackbody emitter, a tube filled with chlorophyll actually allows more red light to pass through than blue light. Actually, you can do this with a light bulb and a test tube full of centrifuged chlorophyll - put the light next to your head, hold tube in front of your face - the tube appears to be filled with green fluid. Put the tube between your face and the light, you see mostly red.

the peak being around 670 nm. Blue light is only required for
physiologicial and morphological responses.
Red is required for photomorphogenesis, root development, and for vegetative growth. Blue is for control of certain day-night reactions, seasonal identification, and most importantly, for actual plant growth and bulk. This is why CMH and MH are the recommended primary HID light source by large commercial-scale horticultural operations, and not HPS.

Again, all the studies I've read say between 8 and 20% of your light should be blue - depending on the plant.
Those NASA-conducted studies are old, and they recanted half of them, their new panel design has 33% blue, 67% red.

Also, flowering is a phytochrome response. It is triggered by the length of the dark period - not by the blue:red ratio of light.
That again depends on the species of plant - The phytochrome can also respond to the ratio of red versus blue and the intensity of both wavelengths in order to determine seasonal changes.

Weed is a short day facultative plant. If you have long dark periods you will be able to accelerate (or short nights will slow) flowering but it will eventually flower regardless of the light color/duration.
No, it will not eventually flower without regard to light color or duration unless you're growing a Ruderalis. How do you think we keep mother plants for decades?

I really don't understand why so many people have this misconception.
I think you have the misconception. I do this across the globe and don't get paid to be wrong. If I was wrong and selling a bad product, I'd have been sued already.

Show me this latest NASA panel design too. I might have to eat my words here in the next few days. :P
I knew I should have saved that picture or site link, because my panel manufacturer couldn't believe it either - but they were growing some sort of lettuce (THICK AS HELL) under 1:2 blue:red light. It's on one of the mission pages I was browsing through earlier this morning. I know it wasn't the PESTO mission page. Drat, which one was it?

Rest assured, more blue is the way to g - why else would manufacturers of those UFO LEDs with the "optimized" 7:1:1 ratio be suddenly selling 'supplementary' blue panels - if the ratios were optimized to begin with, why do you need a supplementary panel?

Also, the guy "stra8outaweed" on the forums will testify - more blue = better yield. Check his grows out.