PPFD

PPFD (Photosynthetic Photon Flux Density) defines the density of the photon flux in the 400–700 nm range incident on a given surface. It is usually expressed in micromoles per square meter per second (µmol m⁻² s⁻¹). PPFD is an instantaneous measurement, whereas the daily amount of light is described by the DLI index. This parameter is more useful than lumens and lux when designing lighting LED for seedlings and crops grown under cover. PPFD should be measured at leaf height at several locations, and the lamp positioning should be adjusted based on the duration of illumination and observations of the seedlings.