I've just spent hours reading through this thread. And The one thing I see people ignore over and over again is the room/tent reflectivity or lack there of. Although I've only anecdotal data, thus not to be considered evidential, my example is a greenhouse. I grew for 2 years in a small greenhouse with a clear cover. I had some nice grows in it. Then I replaced it with a opaque, white, cover. BOOM! My harvests at least doubled! Nothing else change, same strains, my exact same organic soil, the water, location and orientation, all the same. It certainly took me by surprised. I expected less harvest for more security.
I credit the diffuse, even light. Maybe I'm missing something. So why wouldn't that hold true in a growroom/tent? It makes me think in a tent at least, no lenses/reflectors would work as well or better because of the amount of reflected light. Yes, more loss is a factor. But the increase of light from many angles would be increase light striking more leaf surface, possibly more than making up for the losses. Has anyone one done a with/without in a tent comparing grows of clones all from the same mother?
I'd think that would at least give an inkling as to which method is best in a tent, which is what many of us are growing in. I've no doubt in an open room, lenses/reflectors would be the way to go. Even then, I've seen pics here of open rooms that REALLY need a nice whitewash....!
Guess I need to test this by running my light without the lenses, which I just plain don't like, for no good reason.....lol