"Marijuana plants like direct, intense sunlight. Unfortunately LEDs aren't very scalable. As you increase the current they start to run into physical limitations and the efficiency goes to hell. A 100W led may only put out 50lm/W, where a 1W led could put out 100lm/W."
I'm sorry, we've got plenty of LED systems out there pushing 2,000+ umol from several feet away, like any HID. And typical 100w LEDs are about 130 lumens per watt. Cree has LEDs available for the consumer that at 1w drive get 200+ lumens per watt (Cree MK-R) We figured out the Auger/watercooler effect and are working around it. We've got LEDs that dump 150+ lumens per watt at 5-10A drive current, now (Cree XPG2.)
"HIDs are actually extremely efficient (Around 100lm/W) and scalable (bulbs go up to 1kw+)."
We've got 1,000w LED packages in 70mm x 70mm size, with better efficiency.
" To get and equivalent amount of light out of LEDs with some sense of efficiency, you'd need thousands of them."
Plants care about photon flux, not lumens, which is weighted at green wavelengths for human vision. That's not saying that green light isn't useful in itself, but lumens mean jack shit when it's overall photon flux density making the real difference. I'm questioning how out of date your information is. Seems like way early 2000.
And thousands? Seriously?
http://tinyurl.com/mxq5w2b (PDF WARNING)
Try a couple hundred, easily fit on a 30mm x 30mm COB array board. Those are 5W LEDs each. The Cree MK-R is a 15W LED. 100 of those is 1.5kW.
" This may be suitable for plants that can deal with indirect sunlight, but it is not ideal for Cannabis."
Uhhhhhh..... what? Speaking as a medical cannabis user and grower, and as a landrace genetics preservation specialist for a Dutch seed bank, you're totally, absolutely, utterly wrong.