Photosynthetically Active Radiation

The range of light with a wavelength that is from 400 to 700 nanometres which is used by green plants in the process of photosynthesis. Chlorophyll a and chlorophyll b capture light in the blue and red spectrums. Other pigments, the Carotenoids consisting of Carotene and Xanthophyll, are highly active at 450 to 500 nanometres, and typically produce the respective orange and yellow colours of autumn leaves. The main reason for this is that they do not decay as rapidly as the green colour of leaves. The term is frequently abbreviated to PAR.