Daily Light Integral (DLI) Calculator

Convert light intensity (PPFD) and daily light hours into Daily Light Integral — the total moles of photosynthetic light your plants receive each day.

Quick Facts

Formula
DLI = PPFD × hours × 0.0036
3600 seconds per hour ÷ 1,000,000 µmol per mol = 0.0036. Result is in mol/m²/day.

Your Results

Calculated
Daily Light Integral
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mol/m²/day
Light band
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Typical crop suitability

Ready

Enter your PPFD and daily light hours, then calculate.

What is Daily Light Integral (DLI)?

Daily Light Integral (DLI) is the total amount of photosynthetically active radiation (PAR) that a plant receives over a full day, measured in moles of photons per square meter per day (mol/m²/day). Where PPFD tells you how bright the light is at a single instant, DLI is the sum of that light across every second of the photoperiod. It is the single most useful number for describing how much light a crop actually gets — it combines both intensity and duration into one figure that correlates directly with photosynthesis and growth.

The DLI formula

DLI is calculated from PPFD (photosynthetic photon flux density) and the photoperiod (hours of light per day):

DLI (mol/m²/day) = PPFD (µmol/m²/s) × photoperiod (hours) × 3600 ÷ 1,000,000

The two constants come from unit conversion, not from any biological model: there are 3,600 seconds in an hour, and 1,000,000 micromoles (µmol) in one mole. Combining them gives the shortcut multiplier 0.0036, so the formula simplifies to:

DLI = PPFD × hours × 0.0036

For example, a canopy under 400 µmol/m²/s for 14 hours a day receives 400 × 14 × 0.0036 = 20.16 mol/m²/day.

Why DLI matters

Two grow setups can have the same instantaneous PPFD yet deliver completely different amounts of light: 600 µmol/m²/s for 10 hours (21.6 mol/m²/day) versus 300 µmol/m²/s for 20 hours (21.6 mol/m²/day) end up identical, while 600 µmol/m²/s for 18 hours delivers nearly twice as much. Because plant growth responds to the cumulative daily light dose more than to peak intensity, DLI lets growers compare greenhouses, grow tents, and field sites on equal footing and dial in supplemental lighting.

Typical DLI reference points

  • Low-light houseplants (pothos, ferns, snake plant): roughly 2–6 mol/m²/day
  • Lettuce and leafy greens: about 12–17 mol/m²/day for good heads
  • Herbs (basil, cilantro): around 12–18 mol/m²/day
  • Fruiting vegetables (tomato, pepper, cucumber): 20–30 mol/m²/day for strong yields
  • Cannabis flowering / high-light crops: 30–45+ mol/m²/day
  • Full summer sun outdoors: commonly 40–60 mol/m²/day at midlatitudes

Frequently Asked Questions

What is the DLI formula?
DLI (mol/m²/day) = PPFD (µmol/m²/s) × photoperiod (hours) × 3600 ÷ 1,000,000, which simplifies to PPFD × hours × 0.0036. The 3600 converts hours into seconds and dividing by one million converts micromoles into moles, so the answer comes out in moles of photons per square meter per day.
What is the difference between PPFD and DLI?
PPFD is an instantaneous measurement — the number of photosynthetically useful photons landing on a square meter each second (µmol/m²/s). DLI is the total accumulated over an entire day (mol/m²/day). PPFD tells you how bright it is right now; DLI tells you how much light the plant got by the end of the day, which is what drives growth.
What is a good DLI for plants?
It depends on the crop. Low-light houseplants and leafy greens do well at roughly 6–12 mol/m²/day, most vegetables and herbs want 12–20 mol/m²/day, and high-light fruiting crops like tomatoes, peppers, and cannabis want 20–40+ mol/m²/day. Below about 5 mol/m²/day most crops grow slowly, stretch, or fail to flower.
How do I measure PPFD for this calculator?
Use a quantum PAR meter (or a calibrated app-based sensor) held at canopy height, pointing up toward the light source. Take several readings across the canopy and average them, since light is rarely uniform. Use that average PPFD together with the number of hours your lights (or the sun) are actually on the plants.

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