PPFD

PPFD (Photosynthetic Photon Flux Density) measures the amount of photosynthetically active light landing on a surface, in micromoles per square meter per second (µmol/m²/s). It's the meaningful way to gauge grow-light intensity, far better than wattage. Targets rise through the grow: roughly 200–400 for seedlings, 400–600 in veg, and 600–900+ in flower (with CO2 supplementation supporting the high end). Measuring PPFD prevents both under-lighting and light burn.