In the broad sense, photosynthetically active radiation (PAR) is the part of electromagnetic radiation that can be used as the source of energy for photosynthesis by green plants. Technically, it is defined as radiation in the spectral range from 400 to 700 nm. It is expressed either in terms of photosynthetic photon flux density (PPFD , μmol photons m−2 s−1), since photosynthesis is a quantum process, or in terms of photosynthetic radiant flux density (PAR irradiance, W m−2), more suitable for energy balance studies. A fundamental term in the quantification of light used by plants in the photosynthesis process is the fraction of absorbed photosynthetically active radiation (fAPAR) calculated as the ratio of absorbed to total incident PAR in a vegetation canopy. This variable is widely used in vegetation functioning models at a range of spatial scales from the plant to the globe as an indicator of the amount of energy available for photosynthesis.
|Title of host publication||Encyclopedia of Sustainability Science and Technology|
|Editors||Robert A. Meyers|
|Publication status||Published - 2012|
|MoE publication type||D2 Article in professional manuals or guides or professional information systems or text book material|