How this calculator works
PPFD counts photosynthetically active photons arriving each second on a square metre. Multiplying the time-averaged PPFD by the illuminated seconds and dividing by one million converts micromoles to moles. Under changing sunlight, use an integrated sensor reading or a representative time average rather than the midday peak. Lighting hours cannot exceed a day.
Formula
DLI (mol/m2/day) = PPFD (umol/m2/s) × hours × 0.0036. PPFD = DLI/(0.0036 × hours).
Worked example
An average PPFD of 500 umol/m2/s for 16 hours supplies 28.8 mol/m2/day. The same PPFD over 12 hours supplies 21.6 mol/m2/day.
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Frequently asked questions
Can I enter a lux reading?
Lux weights light for human vision. Converting lux to PPFD requires the spectrum of the light source; use a quantum sensor when possible.
Should I use peak PPFD?
Use average PPFD over the specified lighting period. A peak reading overstates daily light when intensity varies.
Does a higher DLI always improve growth?
No. Crop, cultivar, temperature and photoperiod requirements matter. This page converts light exposure and does not prescribe a crop target.