The fact is that a high power HID requires a spacing from plants otherwise they will burn. Lower power lights do not require that space, so more plants can fit within the same room. The best use of a space from my reading and knowledge, not experience would be a shelved warehouse with top lighting. That way vertical space isn't wasted with the top lighting design. Also tends to be the design used in the biggest hydro companies.
Lower power lights also lack in intensity and require closer placement and constant repositioning to remain effective. Not to mention, that even distribution of light like you're suggesting means a lot more, less powerful lights, which means effectiveness is limited by space, with a small tubular shape being most efficient (hence the trashcan).
So, when I was in college the best use of space for me was that trashcan. But now that I have more space and want to run vert, it makes no sense to purchase hundreds of smaller lights that are going to need constant adjustmant and monitoring, not to mention the costs involved here. Instead of keeping a multitude of smaller lights hanging around my canopy, I'd rather position my canopy with optimum distance of a hanging HID bulb.
If I wanted to pull more than a pound a plant I could set up a 12x12 room where P is a plant (vert tree) and X is an HID. Each plant on this scenario is receiving tridirectional HID lighting, much more effective and intense than CFLs or LEDs could ever get.
X P X
P X P
X P X
All these lights have their niches, but CFL and LED don't, IMO, have much of a place in large scale vertical setups because of inherent limitations of the techs themselves coupled with need for high intensity lighting.
The only reason the trashcan works as effectively as it does is because the can is only 2ft across. With multiple points of light distribution on the inside I can be sure that a plant inside is covered with light. But start to increase the diameter of the space and you begin running into problems with keeping a consistent (in intensity) level of light within the space. The solution become High Intensity Discharge lighting, and placing plants around the bulb, or bulbs in between plants.
I think the gains from vert would offset the loss of a few square feet of space, not to mention the whole concept of vert is to more efficiently use the same square footage anyways...
