Definition of Photosynthetically Active Radiation

Photosynthetically active radiation (PAR) is defined as the amount of light that is available for the process of photosynthesis. The wavelength of the light ranges from 400 to 700 nm. The light radiations are highly dependent on the seasons, latitude, and the time of the day. The rate of photosynthesis is greatest during the mid-days of summers due to high PAR and at nights, the value of PAR is zero.


The shades of trees, cloud covers, and buildings are the hindering factors that reduce the rate of photosynthesis to a great level. Air pollution also reduces the rate by filtering out the amount of light. When PAR is high, the growth of plants is highly promoted.

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