A little common sense goes a long way on this subject. Growing with LEDs is just like growing with any HID...IT ONLY WORKS IF YOU KNOW WHAT YOU'RE DOING.
I played around with two cheapo 90w UFOs in a small box with only two plants. Grew them start to finish under only these lights, and like someone said above, the plants stayed healthy throughout the grow, but the buds produced were lose, fluffy, small, and generally just crappy as far as yield.
More recently, in the same box, I grew two more plants with a nice, high quality 300w panel, and the bud quality and yield were comparable to any proper HID grow(flowering took slightly longer to finish). I plan to put five plants under it in a larger area next time, but I have yet to test variables and find out exactly how far you can push a single 300w panel. I'm guessing it comes down to needing a lot more lights for a given area when using LED compared to HID, simply because of the way light is distributed in each. If you're a serious grower willing to drop thousands of dollars to light your entire grow area, then LED is probably the way to go because you will eventually save the money you spent in electric bills. I could have purchased three 1000w HPS setups for what I spent on a single 300w LED panel.
It comes down to how you grow. In the long term the investment is worth it, short term it clearly is not.
One other thing I would like to point out is that when dealing with LEDs you can't judge jack shit from lumen output. The whole theory of growing with LEDs is the fact that they can deliver far more usable spectrum with less lumens...fewer lumens = less energy. Less energy = saving $$ (or so the theory goes).
The only thing I can be certain of right now in regards to growing with LED lights, is that it is excellent supplemental lighting. Those two cheapo UFOs I mentioned earlier are now being used in one corner of a large room, and the plants in that corner of the room are growing with slightly (but noticeably) more vigor than the rest of the room...and the rest of the room looks good. Most of what HPS and MH lights put out is not usable, so adding some extra usable spectrum in there is definitely a good thing.
Obviously a dinky little 90 watt UFO isn't going to compare to a 600 watt HPS. In fact if all you can afford is a 90 watt LED or a 600 watt HPS, I'd say it's a no brainer...
Edited by onlyoneman, 13 May 2010 - 01:57 AM.