Photosynthetic Photon Flux Density (PPFD) is the metric used to measure PAR over a square meter. It is a total count of light energy (in photons) from 400nm to 700nm that reaches a particular point on a plane.
Photobiological Photon Flux Density (PBFD) is the metric used to measure PBAR over a square meter. It is a total count of light energy (in photons) from 350nm to 800nm (or the PBAR range used) that reaches a particular point on a plane.
PPFD and PBFD are both expressed as μmol/m2-sec. See how PPFD and PBFD are measured below.