Plants only use some of the spectrum of light. You want to select the LEDS that emit these.

Good article here:

"The most readily available light from the sun is in the middle spectrums which we see as green, yellow and orange. These are the primary frequencies that human eyes use. However, studies show that these are the least used light frequencies in plants. Most of the photosynthetic activity is in the blue and red frequencies."

Lots of graphs and data here, probably can't finish and digest this article in one bathroom sitting.