DLI Calculator (Daily Light Integral)
Convert PPFD and photoperiod into mol/m²/day for any crop.
Result
Crop DLI ranges are general guidance and assume healthy plants and adequate CO₂; cultivar and stage shift the ideal.
History
What it is
Daily Light Integral (DLI) is the total amount of usable (photosynthetic) light a plant receives over a full day, expressed in moles of light per square metre per day (mol·m⁻²·d⁻¹). It combines light intensity (PPFD) with how many hours the light is on, giving the single best number for whether a crop is getting enough light.
Who should use it
Anyone with a PAR/PPFD meter (or a light with known PPFD) who wants to match their canopy light to the needs of a specific crop and avoid both under- and over-lighting.
How to use it
- Measure or look up the PPFD at canopy height in µmol·m⁻²·s⁻¹.
- Enter the photoperiod — the number of hours the light is on each day.
- Read the DLI in mol·m⁻²·d⁻¹.
- Compare it against the recommended DLI range for your crop and adjust intensity or hours.
Example calculation
Worked example
A canopy receiving 600 µmol·m⁻²·s⁻¹ for 18 hours a day gets a DLI of about 38.9 mol·m⁻²·d⁻¹ (600 × 3600 × 18 ÷ 1,000,000). That suits a high-light crop in vegetative growth; leafy greens would be over-lit at this level.
Formulas used
DLI = PPFD · 3600 · hours / 1,000,000 (mol·m⁻²·day⁻¹)
How to read your result
If your DLI is below the crop range, raise intensity or extend the photoperiod. If it is above, plants may show light stress or simply waste energy and money. Two setups with very different PPFD and hours can deliver the same DLI.
Recommended ranges
| Crop | Target DLI (mol·m⁻²·d⁻¹) |
|---|---|
| Lettuce / leafy greens | 12 – 17 |
| Herbs | 14 – 20 |
| Seedlings / clones | 10 – 20 |
| Tomatoes / peppers | 20 – 30 |
| High-light crops (flower) | 30 – 45 |
Common mistakes to avoid
- Measuring PPFD at the light instead of at canopy height.
- Assuming more light is always better — past a crop's saturation point you pay for electricity with no extra yield.
- Ignoring the photoperiod; the same PPFD over 12 vs 18 hours gives very different DLI.
- Using a single canopy point — light falls off toward the edges of the footprint.
Frequently asked questions
What is a good DLI?
It depends on the crop: roughly 12–17 for leafy greens, 20–30 for fruiting vegetables, and 30–45 for high-light crops in flower. Match your DLI to the plant, not a universal number.
How do I convert PPFD to DLI?
DLI = PPFD × 3600 × hours ÷ 1,000,000. The 3600 converts per-second to per-hour, and dividing by a million converts µmol to mol.
Can DLI be too high?
Yes. Above a crop's saturation point extra light causes bleaching or stress and wastes electricity without raising yield.
Is DLI the same as PPFD?
No. PPFD is instantaneous intensity; DLI is the daily total. DLI = PPFD combined with photoperiod.
Does DLI account for light spectrum?
No. DLI measures photosynthetic photon quantity (400–700 nm), not spectral quality. Spectrum still matters for plant response.