DLI calculator
Enter the PPFD at your canopy and how many hours the light is on, and get the daily light integral (DLI) — the total light the plant receives per day — with a check of the PPFD against the stage target. Free, no signup.
How to use it
- Measure PPFD at the top of the canopy with a PAR/PPFD meter (several points if you can, then use the average).
- Enter the PPFD in µmol/m²/s and the photoperiod in hours per day.
- Choose the stage: the calculator fills a typical photoperiod (16 h seedling, 18 h veg, 12 h flower) that you can change.
- Read the DLI and whether the PPFD is below, within or above the stage target.
How the number is calculated
DLI (mol/m²/day) = PPFD (µmol/m²/s) × hours of light × 3600 ÷ 1,000,000.
PPFD targets used by the calculator: seedling 180–320, vegetative 400–650, flowering 600–900 µmol/m²/s, for photoperiod plants without added CO₂.
DLI depends on hours as much as on intensity: the same 600 PPFD gives 25.9 mol at 12 hours and 38.9 mol at 18 hours.
Quick DLI table (mol/m²/day)
| PPFD | 12 h | 18 h | 20 h |
|---|---|---|---|
| 200 | 8.6 | 13.0 | 14.4 |
| 300 | 13.0 | 19.4 | 21.6 |
| 400 | 17.3 | 25.9 | 28.8 |
| 600 | 25.9 | 38.9 | 43.2 |
| 800 | 34.6 | 51.8 | 57.6 |
| 1000 | 43.2 | 64.8 | 72.0 |
In the GrowScope app
The app uses the same DLI formula with the photoperiod of the plant's own box. Its PPFD target keeps the stage's daily light the same when the photoperiod changes — an autoflower at 20 hours gets a lower PPFD target than at 18 — and rises by 20% (capped at 1300) when you log fresh CO₂ of 900 ppm or more.
Questions
What DLI do cannabis plants need?
With this calculator's targets and typical photoperiods, that is roughly 10–18 mol/m²/day for seedlings, 26–42 in veg at 18 hours and 26–39 in flower at 12 hours.
How many hours of light do I need for a DLI of 40?
Hours = DLI × 1,000,000 ÷ (PPFD × 3600). At 600 PPFD that is about 18.5 hours; at 900 PPFD about 12.3 hours.
Can I use a phone app instead of a PPFD meter?
Phone light apps give rough readings that depend on the phone's camera and calibration. They are fine for relative checks; for absolute PPFD a PAR meter is more reliable.
Is DLI the same as PPFD?
No. PPFD is the light intensity at one moment; DLI is the total over the whole day. Two setups with the same PPFD can give very different DLI if the light hours differ.
Can I put this calculator on my website?
Yes. The widget is free to embed with an iframe; the code is in the guide linked below.