Apogee Instruments Inc.Published on Jun 27, 2019 Dr Bruce Bugbee, president of Apogee Instruments and professor at Utah State University, explains the differences and evolution of the terms PAR (photosynthetically active radiation), PPF (Photosynthetic Photon Flux), PPFD (Photosynthetic Photon Flux Density), and PFD (Photon Flux Density). The meaning of these terms are often misunderstood and […]