This video is incredible. The presenter is very knowledgeable, with tons of experience. Admins: I posted this on the LED board first, thought it would reach more people here. Feel free to delete one or the other. Some notes: HPS puts out 50% of its energy in green/yellow light which is not well usable by plants. 40-50% greater efficiency of PAR lighting per watt for LED. Also critiques PAR rating as being at best a better approximation of utility for growing than the lumens measure. Sunlight is surprisingly not necessarily better than artificial, because of the narrow areas of spectrum that are actually used by plants. Green light actually aides penetration. Fascinating discussion on varying spectrum ratios on controlling and directing plant growth. Apparently only 5 to 10 yield advantage possible in weight. Trade off between weight and resin production. Blue favors resin/strength. Suggests 30% blue to 70% red. Says "Nutrients don't help" (of course, he's a light expert). UVB addition greatly increased THC production. 25% to 32%, single strain. 33 microwatts/cm2 was optimal DO NOT WANT TO WORK WITH UVB WITHOUT PROTECTION. Volumetric theory of canopy management and light management. Reasons not to do SCROG. This video is The Best Single Thing on weed growing I have ever seen. Major changes coming to my next indoor crop. I now have to admit that I have likely been wrong on my beliefs about defoliating. I need a hug.