FeaturedNews in FocusPlant Cuttings New form of photosynthesis that’s above par PAR is the acronym for Photosynthetically-Active Radiation, and refers to light with wavelengths of 400 – 700 nm, the so-called visible spectrum, from red to violet. PAR is photosynthetically-active because it... Nigel ChaffeyAugust 14, 2018