I saw a side by side grow UFO lights vs. HID, it took 3 extra weeks to finish with the UFOs. The yield was 100 grams w/ HID & only 66 grams w/ UFOs. The side by side pics showed that the UFO plant really lacked the vigor that the HID plant had. The UFO grown weed was slightly less potent according to the growers info, of course that I had to leave to trusting his word but the pictures showed the rest of the above to be true otherwise.
The grow was done from clones so that they were exactly the same. It was a soil grow and a large cabinet was split in two so that the environments were also exactly the same.
LEDs have a ways to go imo but do have those two BIG advantages of course, near zero heat and low power consumption. That grower used only two UFO units, perhaps if he had used six (or more) of them he'd have gotten better results but then the cost of each unit as I recall was quite steep.