PPF – Photosynthetic Photon Flux – is the total number of photons that is emitted from a light source. In other words, PPF determines how much photosynthetic active radiation is generated by the luminaire per second. The result of the PPF parameter is expressed in umol / s.
PPFD – Photosynthetic Photon Flux Density – this is the number of photosynthetic photons that fall on a given surface every second. Colloquially, we can define this as the amount of light that actually reaches the plant. PPFD is a site specific measurement and is measured in micromoles per square meter per second – umol / m2 / s. This parameter should always be supplemented by the distance between the surface and the light source and the location, and whether it is an average value for a given area. Without knowing this information, no meaningful comparison of the PPFD values is possible.