Light quality refers to the wavelengths of light in the visible spectrum between 400 and 700 nanometers. Sunlight provides a full spectrum of light, but supplemental light can have a limited wavelength range. For instance, incandescent lamps have mostly red wavelengths while fluorescent lamps have more blue light.

Phytochrome pigments absorb in the red (660 nm) and far red (730 nm) and photosynthetic pigments (chlorophyll) absorb in the blue-green as well as red wavelengths.

Chart showing light absorption of Chlorophyll b across range of wavelengths with peak between 450 to 500 nanometers.