Tools / Lighting

PPFD to DLI calculator

Daily light integral is the documented horticulture measure of how much photosynthetically active light a plant receives over a 24-hour cycle, expressed in moles of photons per square meter per day. The calculator below converts a canopy-level PPFD reading — the instantaneous photon flux density measured at the leaf surface — into DLI by integrating across the photoperiod. The formula is the standard unit conversion used in published cannabis lighting protocols. PPFD describes the intensity at a single moment; DLI describes the daily dose, and it is the figure documented as most reliably predicting growth rate and bud weight at hobby scale.

How the calculation works

PPFD is measured in micromoles of photons per square meter per second (µmol·m⁻²·s⁻¹). Converting to a daily integral requires multiplying by the number of seconds the light is on per day and then dividing by one million to scale from micromoles into moles. The formula is DLI = PPFD × hours × 3600 ÷ 1,000,000, where 3600 is the documented number of seconds per hour. A canopy receiving 600 µmol·m⁻²·s⁻¹ for 18 hours therefore receives roughly 38.9 mol·m⁻²·day⁻¹.

The calculation assumes the fixture maintains a flat PPFD across the photoperiod, which is documented as accurate for LED panels at fixed output and approximately accurate for HPS once the bulb is up to temperature. Dimmable fixtures running ramped schedules deliver less than the nameplate figure suggests; in those rooms, the documented procedure is to average the PPFD reading across the actual on-time rather than using peak intensity.

Reference ranges

Documented cannabis DLI targets are commonly split into four stage windows. Seedlings and clones are documented as wanting under 20 mol·m⁻²·day⁻¹, a low-stress establishment dose that protects emerging root systems. Vegetative plants are documented as performing best between 20 and 30 mol·m⁻²·day⁻¹, the published window for sturdy leaf and stem expansion without burn. Flowering plants are documented as wanting 30 to 50 mol·m⁻²·day⁻¹, with the upper end producing the documented densest, fattest buds when paired with adequate CO2 and nutrition.

Anything above 50 mol·m⁻²·day⁻¹ is documented as saturation territory — light becomes the surplus rather than the limiting factor, and the published payoff disappears unless ambient CO2 is raised from atmospheric 400 ppm toward the 1000-1200 ppm range. Most home tents are documented as finishing strong at 35 to 45 mol·m⁻²·day⁻¹.

Related references: Lighting · Vegetative stage · Flowering stage

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