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PPFD - Photosynthetic Photon Flux Density is the photon flux density of PAR. Measured in
either umls or uE., PPFD, or “photosynthetic photon flux density”, is the number of PAR
photons incident on a surface in time and area dimensions (per meter squared per second).
These terms are equivalent for PAR Clip leaf radiation measurements. Furthermore, both can
be presented in either of the equivalent dimensions, micro-moles (µmols) or micro-Einsteins
(µE).