I remember researching this a while back and i found some info on the green wavelength.. Plants dont "use" the spectrum for growth directly, and thus it is typically safe to have a solid green light on in your grow room when the lights are off (green LEDs included). But... when the lights are on the green is said to help the plant use light more effectively. Some of the more expensive LED grow lights are starting to incorporate green into the spectrum mix because of this.. I personally just bought a few Blackdog Micro-U lights that have a few green bulbs.. The seem to be working really well! Im at about week 5 of flowering and they are easily keep pace with my 1000w hps for quality and density of bud.. Intersting stuff the science of light!