I just finished vegging 8 plants in a 20 sq ft area with four, 28 watt LED panels. They worked great. Compact growth, tight nodes and very healthy plants.
However, I've not flowered with them yet, so like most of the others who answered and also haven't used them for flowering, it would be a guess for me to tell you how they would work.
I don't think I would risk a crop by testing them. I would grow a standard HPS flowered crop and test one LED on one plant in a box of its own. Then, if it doesn't work, you're out only the cost of one LED and some time.
As far as LED experience goes, you're going to get a bunch of variations of:
1. No, I haven't tried it but it suks.
2. No, I haven't ever done it, but it won't work.
3. No, I've never even tried it, but I've heard it suks.
4. No, I've never tried it, but I saw some pics once and it suks.
5. No, I've never done it, but the buds will be light and airy.
6. No, I've never tried it, but save your money and do it the standard way.
In regards to LEDs, rumor, second-hand stories and opinion is 99% of what you'll get if you ask about them. Those who have actually tried them, (like me), love them for vegging and have never even tried them for flowering.
I'm going to try one plant in a 30" x 30" x 36"H box with a 28 watt LED panel and take it from rooted clone to harvest. I'll start a thread for it when it is started. The title of the thread will be something like "28 watt LED flowering trial".
Good luck man. If you try one, please post your experiences.
