Daily Light Integral Calculator
Daily light integral — the moles of photons a square metre of crop receives in a day — from the meter’s PPFD and the hours of light.
PPFD is measured in micromoles of photons per square metre per second.
How the daily light integral calculator works
PPFD is measured in micromoles of photons per square metre per second. Multiply by seconds of light in the day and divide by a million for mol/m²/day. Lettuce is content at 12–17, tomatoes and cannabis want 25–40+, seedlings 6–10. Enter your target and the calculator gives the hours needed at this intensity, or the intensity needed for these hours.
Formula: DLI = PPFD × hours × 3,600 ÷ 1,000,000
Worked examples
| Inputs | Daily light integral | Note |
|---|---|---|
| 400 µmol for 16 hours | 23 mol/m²/day | 23.0 mol |
| Full sun, 2,000 µmol for 8 hours | 57.6 mol/m²/day | 57.6 mol |
| Seedlings at 150 µmol, 14 hours | 7.6 mol/m²/day | 7.6 mol |
FAQFrequently asked questions
What DLI do plants need?
Seedlings and shade plants 6–10 mol/m²/day, leafy greens 12–17, herbs 15–25, fruiting crops like tomatoes and peppers 25–35, cannabis 35–45. Outdoors, full summer sun delivers 40–60.
How do I measure PPFD?
With a quantum (PAR) meter at canopy height, reading µmol/m²/s. Phone apps are rough, and lux meters need a conversion factor that depends on the light source.
Is more light always better?
Only up to a point: photosynthesis saturates, and beyond it extra light is heat, electricity and sometimes bleaching. Match DLI to the crop rather than maximising it.
Should I lengthen the photoperiod or raise the intensity?
Both give the same DLI, but some plants are photoperiod-sensitive — they flower on day length — so intensity is the safer lever for those.
Where these figures come from
- NCBI Bookshelf — Molecular Biology of the Cell — growth kinetics and molecular conventions
- CSIRO — Australia's national science agency
Last checked: September 2026. Formulas are the standard textbook forms; assumptions are stated on each page because they are where these models break.