free calculator
DLI Calculator
Enter the light intensity (PPFD, in µmol/m²/s) and how many hours of light per day — the calculator shows the DLI, the total amount of light your plant receives over the day.
resulting DLI
— mol/m²/day
What DLI is and why it explains more than PPFD
PPFD is a snapshot, DLI is the movie
PPFD measures light intensity at a single moment — how many photons land on an area per second. But the plant doesn't live in moments: it accumulates light across the entire photoperiod. DLI (Daily Light Integral) adds up that intensity over the hours of light in the day and gives you a single number — the total useful light the plant received, in moles of photons per square meter per day.
Why this beats looking at PPFD alone
Two tents can share the same PPFD and end up with completely different growth if the photoperiod differs — 18 hours of light at 400 µmol/m²/s deliver almost twice the total light of 10 hours at the same intensity. DLI combines both variables into one measurement, and it's that measurement that correlates best with growth rate and plant morphology.
How to use the number you calculated
Compare the DLI you calculated with the reference range for the current stage (table below). If it's well below, consider moving the light closer, raising the intensity, or stretching the photoperiod gradually. If it's well above, watch for signs of light stress — pale leaves at the top of the canopy, stalled growth — and consider raising the light.
DLI ranges by stage (reference)
Approximate ranges — cultivars, genetics and setups vary a lot. Raise the DLI gradually when changing stages so you don't shock the plant.
already logging light intensity in your diary?
The GrowerHelper app logs PPFD or lux readings per event and calculates DLI automatically from your grow's photoperiod — with a chart of how it evolves over the cycle. All offline, no signup.