DLI (mol/m²/day) = PPFD × Hours × 3600 / 1,000,000
Daily Light Integral (DLI) is the total photosynthetically active radiation (PAR, 400-700nm) received by a plant in one day, measured in mol/m²/day. DLI = PPFD (μmol/m²/s) × photoperiod (hours) × 0.0036. DLI requirements vary: lettuce 12-17, tomatoes 20-30, roses 20-30, cannabis 35-45 mol/m²/day. Full summer sun provides DLI 40-60 in mid-latitudes. Indoor growers adjust PPFD and photoperiod to achieve target DLI. More light generally means more growth — until the light saturation point. DLI is better than instantaneous PPFD for comparing lighting strategies because it accounts for both intensity and duration. Many commercial greenhouses use DLI targets to control supplemental lighting.