Photosynthetically Active Radiation (PAR) values determine the growing strength of a light.  PAR is expressed as Photosynthetic Photon Flux (PPF). PPF is the total light (photons) emitted by a light source each second.

PPF tells us how much PAR is emitted by a light source and is measured in micromoles per second  (μMoles/second).  Natural sunlight has a PAR value of 1200-1500 μMoles/second.