Blue and red light are absorbed by plants and have the greatest effect on plant growth. They are therefore critically important for young plants. Blue light is responsible primarily for vegetative (leaf) growth. Red light, when combined with blue light, encourages flowering (so blue light is important for this, too). Then there´s green light, which plants reflect rather than absorb, thereby making plants look green to our eyes.

Chlorophyll absorbs red light, and some of the accessory pigments absorb blue light. Plants do not absorb green light, or light outside of the visible spectrum.