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Calculate daily light integral from PPFD and photoperiod for optimal plant growth
PPFD (\μmol/m\²/s)
Measured at canopy level with a PAR meter
Photoperiod (hours)
Growth Stage
38.9
mol/m²/day
Target: 20 \– 40 mol/m²/day for veg
DLI Gauge
You're within the optimal DLI range for vegetative growth.
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Create Free Account →Daily Light Integral (DLI) measures the total number of photosynthetically active photons delivered to a square meter of your canopy over 24 hours. It's expressed in mol/m²/day and is calculated by multiplying PPFD (light intensity) by the photoperiod (hours of light).
Think of PPFD as the speed of a faucet and DLI as the total water collected in a bucket over the day. A lower PPFD for longer hours can deliver the same DLI as a higher PPFD for fewer hours. This makes DLI the most reliable way to ensure your plants receive adequate light for each growth stage.
| Stage | Target DLI | Notes |
|---|---|---|
| Seedling/Clone | 12 \– 20 | Gentle light, avoid stress |
| Vegetative | 20 \– 40 | Active growth, increasing light |
| Flowering | 35 \– 55 | Peak light, CO2 helps above 40 |
At ambient CO2 levels (~400 ppm), plants reach a light saturation point around 35-40 mol/m²/day DLI. Beyond this, additional light doesn't translate to additional growth and can cause stress. However, supplementing CO2 to 1000-1500 ppm raises this ceiling significantly, allowing plants to productively use up to 55-65 mol/m²/day. If you're running high-intensity lights, CO2 supplementation is essential to avoid wasting energy.
What is DLI and why does it matter?
DLI measures the total photosynthetic light delivered per day. It's the best single metric for ensuring adequate light because it accounts for both intensity and duration.
How do I measure PPFD?
Use a PAR meter at canopy level, a smartphone app like Photone, or refer to your light manufacturer's PPFD charts.
What happens if DLI is too high?
Excessive DLI causes light stress: bleached leaves, curling, and reduced growth. Stay within recommended ranges unless supplementing CO2.
Does CO2 affect how much light plants can use?
Yes. CO2 supplementation raises the light saturation point, allowing plants to use more light productively.
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