Let me try coming at this discussion from another angle....
I've been growing for 26 years, I never get 2 pounds per light and this is why.....
1) Over the years I have found that strains known for HUGE yields are nowhere close to being the best strains around. I prefer quality over quantity, and thus you won't find strains like Big Bud hybrids and Blue Dream in my grow. I did grow Blue Dream once under 1000W and got a little over 6 oz's off one plant, but it's B+ grade pot and people don't want it. I could probably only fit 6 of those under a single 1000W, but do the math and there's your 2+ pound yield per 1000W.
2) I grow in soil in 5 gal containers. I do not like hydro for a number of reasons. Yes, you can get bigger yields from hydro, but soil grown tastes better in my opinion.
3) My grow is 100% organic. People who are getting the crazy yields mentioned here are using non-organic nutes, at least in part. I'm not inclined to believe anyone who says otherwise though I wouldn't say it's completely out of the question.
4) I like variety and I typically have 3-7 strains going at any given time vs. a mono crop of a big yielding strain.
Frankly, the preference of greedy commercial growers for big yielding strains has hurt the overall quality that we see these days, especially when it comes to outdoor grows. I've exclusively grown indoors for a while now, but I used to grow outdoors in the late 80's and early 90's and there were some DANK strains going around back then. Yes, an outdoor plant would typically yield maybe 1 to 1.5 pounds, but the weed was DANK. I don't see anything like that anymore. Outdoor growers I know these days are 100% concerned about their bottom line (yield). Their gardens are full of massive plants that yield 5-7 pounds of B grade pot that might be good enough for people in New York, but they struggle to get $1000/lb for it on the west coast. So, instead of growing smaller quantities of better weed, they just grow more and more B grade and perpetuate inferior genetics.
What it comes down to is do you want to have the best pot around, or the most pot? Most growers these days seem to choose the latter. If you have a market for B+ grade my hat is off to you. I'm very VERY happy for you. My friends are SUPER picky and if it's not comparable to what you see going for $55-60 an eighth at a club they will turn it down. They definitely keep me on my toes, but that's a good thing.
