اہم حقائق

• Measures light in the photosynthetically active radiation (PAR) range: 400–700 nm
• Unit: µmol/m²/s — how many photons hit one square metre of canopy per second
• Leafy greens thrive at 150–250 µmol/m²/s; fruiting crops need 400–800+
• PPFD varies with distance from the light source — measure at canopy height
• More useful than wattage for comparing grow lights across brands and technologies
• Daily light integral (DLI) = PPFD × hours of light — the total daily photon dose