DLI Calculator
Calculate daily light integral from PPFD and photoperiod, and the PPFD or hours needed to hit a target DLI.
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What this tool does
The DLI Calculator multiplies canopy PPFD by the photoperiod (× 0.0036) to give the total photosynthetic light a plant receives per day in mol/m²/day, and works backwards from a target DLI to the PPFD or hours required.
How to use the DLI Calculator
- Measure or look up PPFD at canopy level (a PAR meter or your light's published PPFD map).
- Enter the hours the lights are on.
- Enter a target DLI for your crop to see what it would take to reach it.
Formula
DLI = PPFD × hours × 0.0036
- 0.0036
- 3,600 seconds per hour ÷ 1,000,000 µmol per mol
- PPFD
- Photosynthetic photon flux density, µmol/m²/s, 400–700 nm
Worked example
800 µmol/m²/s for 18 hours delivers 800 × 18 × 0.0036 = 51.8 mol/m²/day — above the 30 target.
Inputs
- PPFD at canopy (µmol/m²/s)800
- Photoperiod (hours of light)18
- Target DLI (mol/m²/day)30
Result
- Daily light integral51.84 mol/m²/day
- PPFD needed for target DLI463 µmol/m²/s
- Hours needed at this PPFD10.4 hours
Typical DLI targets (mol/m²/day)
| Crop / stage | DLI |
|---|---|
| Seedlings / clones | 6–12 |
| Leafy greens & herbs | 12–18 |
| Vegetative growth (fruiting crops) | 20–30 |
| Flowering fruiting crops | 30–50+ |
| Full-sun outdoor summer day | 50–65 |
Results explained
- DLI
- Total daily photosynthetic light at the canopy.
- PPFD needed
- Intensity that would exactly hit the target in your photoperiod.
- Hours needed
- Photoperiod that would hit the target at your current PPFD.
Frequently asked questions
DLI = PPFD × hours of light × 0.0036. At 600 µmol/m²/s for 16 hours: 600 × 16 × 0.0036 = 34.6 mol/m²/day.
Seedlings thrive at 6–12, leafy greens at 12–18, and fruiting/flowering crops at 30–50 mol/m²/day. More light past a crop's saturation mostly buys heat and electricity bills.
Yes — DLI only counts the daily total, which is why the tool shows the hours needed at your PPFD. Limits: most plants need a dark period, and very low intensity for very long hours underperforms the same DLI delivered brighter.
Lux is weighted for human eyes (green-heavy); plants use 400–700 nm photons roughly evenly. A lux reading can't convert to PPFD reliably without knowing the light spectrum — use the manufacturer's PPFD map or a PAR meter.
They are the two dials of indoor growing: DLI sets how much the plant is asked to work, VPD sets how easily it can transpire while doing it. The VPD Calculator is the companion tool.