Im not knocking leds, thats the point, but i am knocking their claims. Theres a difference and purely based on the equation that yeild is king for a lot of us i think we have a pretty good answer here.
The rest is down to each grower, you wont go wrong with a decent led unit and even less so if you do the research and get help from the growers that use them in building your own from scratch.
Perhaps, cobs are a bit more work to setup properly on a commercial scale, I understand having so much stuff hanging could be a pain on a large scale but at this point I'd be curious to see what would yield the best, 1000w DE or 20 x 50w COBs evenly spread over a 5 x 5. We need someone to do a 5 x 5. When I did my first round with COBS, I was a little disappointed because I thought they were not that bright.
Because of that I squeezed 10 x 90w over a 3 x 4 . Since then I've learned that they are brighter to the plants than they are to us, more usable light. I think my initial reaction to how weak they were had more to do with the 3000k light spectrum.
BTW, that first round had yielded almost 20 ounces of high grade medicine, 3 out of 6 plants were from seeds and the clones were rushed in. It was still a good grow for me at the time.
Since then, I've learned to spread the COBS a little more and also use some as side lighting, they don't need to be as close to the plants than most people think. I shoot for 40-65watts per sq ft and the quality and yields are great.