Photosynthetically Active Radiation (PAR)

Photosynthetically active radiation (PAR) is the part of the solar spectrum between 400 and 700 nanometers that phytoplankton and plants use for photosynthesis, reported as a quantum flux in micromoles of photons per square meter per second or as an energy flux in W/m2. PAR is roughly 45 to 50 percent of total surface solar irradiance. In the ocean it drives primary production and decays with depth following Beer’s law, setting the euphotic zone, conventionally the depth of 1 percent surface PAR. Satellite ocean-color sensors estimate surface PAR and its attenuation, linking the light field to chlorophyll and net primary production.