DLI (Daily Light Integral)

Daily Light Integral (DLI) is the total amount of photosynthetically active radiation (PAR, 400-700 nm) received per unit area over a 24-hour period. It is expressed in moles of photons per square metre per day (mol/m²/day).

DLI is calculated from PPFD (Photosynthetic Photon Flux Density) and the duration of the light period:

DLI = PPFD (μmol/m²/s) × Hours × 3600 ÷ 1,000,000

Understanding DLI allows growers to optimise their light periods, choose appropriate fixtures, and compare natural and artificial lighting conditions.

Typical DLI requirements:

• Propagation / low-light plants: 4-10 mol/m²/day
• Leafy greens / herbs: 12-20 mol/m²/day
• Vegetative cannabis / tomatoes: 20-35 mol/m²/day
• Flowering cannabis / fruiting crops: 35-50 mol/m²/day
• High-intensity crops: 50-65 mol/m²/day

DLI can be increased by raising light intensity (PPFD), extending the photoperiod, or both.