Daily Light Integral (DLI) Calculator
Convert your measured light intensity (PPFD in µmol/m²/s) and daily photoperiod into a Daily Light Integral — the total moles of photosynthetically active photons reaching a plant per square metre per day. DLI is the key metric for optimising plant growth under artificial or natural light.
µmol/m²/s
hours/day
mol/m²/day — total photosynthetically active photons delivered per day
- 1
Photoperiod in seconds
16 × 3600 = 57,600 s/day - 2
Total photons µmol/m²/day
400 × 57,600 = 23,040,000 µmol/m² - 3
Daily Light Integral (DLI)
23,040,000 ÷ 1,000,000 = 23.04 mol/m²/dayDividing by 1,000,000 converts micromoles to moles.
How does this calculator work?
DLI = PPFD × photoperiod (hours) × 3600 / 1,000,000 gives the total moles of PAR photons per m² per day. Most vegetable crops need 10–30 mol/m²/day; high-light crops need 30–50+. Enter PPFD (measured by PAR meter) and light-on hours to check whether your grow environment meets the target.
Formula
How this is calculated
Plants absorb photons in the 400–700 nm range (photosynthetically active radiation, PAR). PPFD is a snapshot: the instantaneous number of PAR photons landing on 1 m² every second, measured in micromoles per m² per second (µmol/m²/s). The Daily Light Integral (DLI) sums all those photons over the entire day and expresses the total in moles per m² per day (mol/m²/day).
Converting units: 1 hour = 3 600 seconds, and 1 mole = 1 000 000 micromoles, so DLI = PPFD × hours × 3600 / 1 000 000. This calculator assumes PPFD is constant throughout the photoperiod — a realistic approximation for LED or HID grow lights with timers, though natural sunlight follows a bell curve through the day.
DLI requirements vary enormously by crop. Leafy greens and herbs thrive at 10–14 mol/m²/day; fruiting crops like tomatoes and peppers need 20–30; high-light crops like cannabis or cacti may need 35–50+. Outdoor DLI in summer mid-latitudes can reach 50–60 mol/m²/day on clear days, while winter or overcast days may fall below 5.
Frequently asked questions
A PAR (photosynthetically active radiation) meter, also called a quantum sensor, measures PPFD in µmol/m²/s. Hold the sensor at canopy level under the light source. Consumer-grade meters cost £30–150; professional meters are more accurate. Smartphone apps using the phone camera give rough estimates only.
Yes — for most vegetative crops you can increase DLI by either raising PPFD or extending hours. However, many flowering plants are day-length sensitive (photoperiod triggers flowering), so extending hours beyond the critical threshold may prevent or delay flowering regardless of DLI. Check crop-specific photoperiod requirements.
In mid-latitudes (40–55°N/S), midsummer outdoor DLI on a clear day reaches 40–60 mol/m²/day. In midwinter it may drop to 3–8. Greenhouse growers use this calculator to decide when supplemental lighting is needed to maintain a target DLI year-round.
TG we-Calculate Editorial Team. (2026). Daily Light Integral (DLI) Calculator [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/daily-light-integral-dli-calculator
TG we-Calculate Editorial Team. "Daily Light Integral (DLI) Calculator." TG we-Calculate. 2026. https://we-calculate.com/calculator/daily-light-integral-dli-calculator.
TG we-Calculate Editorial Team, "Daily Light Integral (DLI) Calculator," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/daily-light-integral-dli-calculator
@misc{wecalculate_daily_light_integral_dli_calculator, title = {Daily Light Integral (DLI) Calculator}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/daily-light-integral-dli-calculator}}, year = {2026}, note = {TG we-Calculate} }
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