The first part of my aeroponics project (overview) is turning those blue and red LED Christmas lights into a grow lamp.
The basic design is a 2 dimensional array of alternating red and blue lights mounted to a piece of white foam board.
Here's a plot of the layout (generated in Octave of course):
And here is the light board as built:
You'll notice two empty holes on the right hand side of the board, the wire between the lights was a really tight fit to meet the spacing I chose (should have checked that a little more closely before drilling all those holes).
Those mini-LEDs look pretty bright, but I'm not sure if it is producing enough light to actually grow a plant, might need to add a string or two. The packaging claims that you can safely plug 43 (!!) of the 60 light strings into a single outlet.