Here it is in a nutshell. What we're all trying to do here is reproduce what happens in nature. The best light for plants is natural sunlight because it is white light, light that contains all of the colors of the visible spectrum (red, orange, yellow, green, blue, indigo, and violet). "Sunlight has an equal balance of the blue and red light rays that plants need. If you grow with both spectrums, you'll be reproducing the suns natural light better than just using one spectrum.