It was the section in the 1/7 video with the different beakers of colored water that went into it, if I remember right. Has to do with the efficiency of the COB's. When the current decreases, the efficiency increases. So you're converting more energy per watt used to photons instead of heat. The theory is that if you run more lights at lower current you'll get more photons than you would with fewer lights at higher current for the same overall watts used. The overall price starts going up typically because of the larger number of COB's used, but at the price that pop22 sniffed out I would think that changes the game a bit.
I only watched a couple of the videos the one time so far, though, so hopefully an expert can correct if I'm off anywhere with all that. :smoking: