About the Daily Light Integral Calculator
This daily light integral (DLI) calculator converts a light intensity reading in PPFD (µmol/m²/s) and the number of hours the light is on into the total photosynthetic light a plant receives in a day, in moles per square meter per day. DLI is the figure growers use to compare a sunny windowsill, a greenhouse bench and an LED grow tent on equal terms.
It is built for indoor gardeners, hydroponic growers and anyone choosing or dimming a grow light. Enter a target DLI for your crop and the calculator also tells you the PPFD needed at your current photoperiod, and the hours needed at your current PPFD. If you only have a lux meter, switch the input to lux and pick the light source to get an approximate PPFD.
Lux-to-PPFD factors are approximations because lux is weighted to human vision, not plant light; a quantum (PAR) meter is more accurate. Readings vary across a canopy, so measure at plant height in several spots and use the average.
With the default inputs, the daily light integral is 23.04 mol/m²/day. Change any value above to recalculate instantly.
How to use the daily light integral calculator
- 1Measure PPFD at the top of the plant canopy with a quantum meter (or enter a lux reading).
- 2Enter how many hours per day the light is on.
- 3Set a target DLI for your crop.
- 4Read the DLI, then adjust light height, dimmer or timer using the PPFD and hours needed.
Formula and method
PPFD (photosynthetic photon flux density) is the number of micromoles of photons in the 400–700 nm range landing on a square meter every second. Multiplying by the seconds the light is on (hours × 3,600) gives micromoles per day, and dividing by one million converts that to moles per square meter per day — the daily light integral.
The same relationship rearranges to give the PPFD needed for a target DLI at a fixed photoperiod, or the hours needed at a fixed PPFD. When you enter lux, it is converted with an approximate factor for the light source (about 0.0185 µmol/m²/s per lux for sunlight); these factors depend on the light spectrum and are only estimates.
- DLI
- Daily light integral, mol/m²/day
- PPFD
- Photosynthetic photon flux density, µmol/m²/s
- Hours
- Photoperiod — hours the light is on per day
Worked examples
400 PPFD for 16 hours
400 µmol/m²/s × 16 h × 3,600 s = 23,040,000 µmol, or 23.04 mol/m²/day — enough for fruiting crops. To hit 17 mol for leafy greens you could dim to about 295 µmol/m²/s, or keep 400 and run the light about 11.8 hours.
Windowsill reading of 20,000 lux sunlight for 12 hours
20,000 lux of sunlight is roughly 20,000 × 0.0185 = 370 µmol/m²/s. Over 12 hours that gives about 16 mol/m²/day, comfortably above a 12 mol target for herbs.
Seedlings at 200 PPFD for 18 hours
200 × 18 × 3,600 ÷ 1,000,000 = 12.96 mol/m²/day. Reaching 12 mol would need 12,000,000 ÷ (200 × 3,600) ≈ 16.7 hours.
Frequently asked questions
What is a good DLI for plants?+
Low-light houseplants manage on about 3–6 mol/m²/day, leafy greens and herbs grow well around 12–17, and fruiting crops such as tomatoes and peppers prefer roughly 20–30. Seedlings typically do well around 10–15.
How do I convert PPFD to DLI?+
Multiply PPFD by the photoperiod in hours and by 3,600 seconds, then divide by 1,000,000. For example, 300 µmol/m²/s for 14 hours gives 300 × 14 × 3,600 ÷ 1,000,000 = 15.1 mol/m²/day.
Can I convert lux to PPFD?+
Only approximately. For sunlight, multiply lux by about 0.0185 to estimate PPFD; for white LEDs the factor is roughly 0.014–0.016. Because lux measures brightness to the human eye, a PAR meter gives far more reliable numbers.
Is it better to raise PPFD or extend the photoperiod?+
Both raise DLI. Longer hours at lower intensity is often more efficient for leafy crops, but many plants need a dark period, and short-day flowering plants need long nights, so check the photoperiod needs of your crop.
What is the DLI outdoors?+
Outdoor DLI ranges from under 5 mol/m²/day on dark winter days at high latitudes to 50–60 or more on clear summer days in sunny regions. Greenhouse glazing typically cuts that by 30–50%.