PPFD (Photosynthetic Photon Flux Density) measures the amount of photosynthetically active light (400β700 nm) delivered to a plant's surface per second, expressed in micromoles per square metre per second (Β΅mol/mΒ²/s). It is the most accurate metric for comparing grow light intensity and effectiveness.
Key Facts
- Measures light in the photosynthetically active radiation (PAR) range: 400β700 nm
- Unit: Β΅mol/mΒ²/s β how many photons hit one square metre of canopy per second
- Leafy greens thrive at 150β250 Β΅mol/mΒ²/s; fruiting crops need 400β800+
- PPFD varies with distance from the light source β measure at canopy height
- More useful than wattage for comparing grow lights across brands and technologies
- Daily light integral (DLI) = PPFD Γ hours of light β the total daily photon dose