Grow science · 04

DLI explained

PPFD is how bright. DLI is how much.

DLI calculator

PPFD micromol/m²/s Light hours per day

DLI · mol/m²/day–

Same DLI at 12 h–

What it is

The daily light integral is the total amount of light a plant receives in one day, measured in mol/m²/day. PPFD tells you how bright it is right now – DLI adds up the whole day.

The formula

DLI = PPFD × hours × 0.0036

0.0036 converts seconds and micromoles into mol per day.

Same DLI, different schedule

600 PPFD × 18 h	38.9
900 PPFD × 12 h	38.9

Fewer hours need more intensity to deliver the same daily dose – that’s why lights go up when the schedule goes down.

Typical targets

Stage	mol/m²/day
Seedlings & clones	10–20
Veg	25–40
Flower	35–45+

For high-light crops. Too little: stretch and small yields. Too much: bleaching and stress.