It is my understanding that not just any
led will do, they need to be a high output LED's. I also understand they aren't exactly cheep at something like $3 to $5 for 1 high output LED. Also just like florescent
lights, the usable light (intensity) they put out drops much faster than HID lighting. So they need to be at close range to be useful. My guess is you will need hundreds of them to see much of anything in the way of improved growth (especially for anything larger than lettuce).