About this tool
Grow Light DLI Calculator is a free, in-browser tool for indoor and greenhouse growers. Enter the measured light intensity (PPFD in µmol/m²/s) and the daily photoperiod in hours, and it returns the Daily Light Integral — the total moles of usable light your plants receive each day. Or switch modes to solve the PPFD or the hours needed to hit a target DLI. Nothing is uploaded; everything is computed locally.
DLI = PPFD × hours × 3600 ÷ 1,000,000, which simplifies to PPFD × hours × 0.0036, in moles per square meter per day. So 400 µmol/m²/s for 16 hours gives 400 × 16 × 0.0036 = 23.04 mol/m²/day. To reverse it, required PPFD = target DLI ÷ (hours × 0.0036) and required hours = target DLI ÷ (PPFD × 0.0036). Enter an optional target DLI in the first mode to see whether your setup meets it.
Use the reference ranges as a starting point: leafy greens 12-17, herbs 14-20 and fruiting crops 20-30 mol/m²/day. PPFD must be measured with a quantum (PAR) meter at canopy height — lux or watt readings do not convert directly, so enter a real µmol/m²/s figure.