DLI Calculator (Daily Light Integral)
Turn PPFD and light hours into daily light integral (DLI). You can also work backwards: enter a target DLI and see how many hours of light you need.
How the calculation works
PPFD is moles-of-photons-per-second, so to get the daily total you multiply by the seconds of light and convert micromoles to moles:
DLI = PPFD × hours × 3,600 ÷ 1,000,000 and hours needed = target DLI × 1,000,000 ÷ (PPFD × 3,600)
Example: 300 µmol/m²/s for 16 hours gives 300 × 16 × 3,600 ÷ 1,000,000 = 17.28 mol/m²/day. To hit a target of 14 with the same 300 µmol/m²/s you would need 14 × 1,000,000 ÷ (300 × 3,600) = 12.96 hours.
The calculation assumes the PPFD is the same all day, which is true for a fixed indoor light. Combine it with the grow light electricity cost calculator to see what a given DLI costs you.
DLI values quoted for crops are general guidance. Read PPFD at plant height, because it falls off quickly with distance from the light.
Frequently asked questions
What is DLI?
Daily light integral is the total amount of photosynthetically active light a plant receives in one day, measured in moles of photons per square metre per day (mol/m²/day). It combines how bright the light is with how long it is on.
What DLI do plants need?
It varies. As a rough guide, leafy greens and herbs often do well from about 12 to 17 mol/m²/day, and fruiting crops like tomatoes and peppers often want more, about 20 to 30. Check the guidance for your crop.
Where do I get PPFD?
PPFD (photosynthetic photon flux density, in µmol/m²/s) is measured at the plant canopy with a PAR meter or a smartphone sensor made for the purpose. Many light makers publish PPFD maps at set distances, which you can use as a starting point. Lux readings are not the same thing as PPFD.
Can I raise DLI by running the light longer?
Yes. DLI goes up with both PPFD and hours, so a dimmer light can reach the same DLI with a longer photoperiod. Plants also need a dark period, so the usual maximum is about 18 to 20 hours for most crops.