PPFD (Photosynthetic Photon Flux Density) is a measure of the amount of usable light that actually falls on a plant . It is measured in micromoles of photons per square meter per second (µmol/m²/s) and indicates how many photons in the PAR spectrum (400-700 nm) a plant receives on a specific surface area.
Why is PPFD important?
🌱 Don't just measure the light a lamp emits (like PPF), but what the plant actually receives.
🌱 Determines the growth rate and photosynthesis efficiency of plants.
🌱 Helps position grow lights for optimal plant growth.
PPFD varies depending on the distance between the lamp and the plant and the spread of the light .
Difference between PPF, PPFD and DLI
| Term | Meaning | Unit | Application |
|---|---|---|---|
| PPF (Photosynthetic Photon Flux) | Total PAR light emitted by a lamp | µmol/s | Amount of light a lamp produces |
| PPFD (Photosynthetic Photon Flux Density) | How much PPF falls on a specific surface | µmol/m²/s | How much light a plant actually receives |
| DLI (Daily Light Integral) | Total PPFD received per day | mol/m²/day | Important for plant growth cycles |
How is PPFD measured?
PPFD is measured with a quantum sensor that counts only photons in the PAR spectrum (400-700 nm) .
- The closer the lamp to the plant, the higher the PPFD .
- The further the lamp, the lower the PPFD .
A uniform light distribution over the entire growing surface is crucial.
How much PPFD do plants need?
Each plant species has an optimal PPFD value for healthy growth.
| Plant species | Optimal PPFD (µmol/m²/s) |
|---|---|
| Seedlings & cuttings | 100 - 300 |
| Vegetables & herbs (growth phase) | 300 - 600 |
| Vegetables & herbs (flowering/fruiting) | 600 - 900 |
| Cannabis (growth) | 400 - 600 |
| Cannabis (flowering) | 600 - 1000 |
| Greenhouses with daylight support | 200 - 400 |
🌞 Full sun has a PPFD of about 2000 µmol/m²/s , but most plants don't need that much.
How does the distance from the lamp affect the PPFD?
🔹 Closer to the plant = higher PPFD but can cause stress (light burn).
🔹 Too far away = lower PPFD and possibly insufficient light for photosynthesis.
🔹 Reflectors and multiple lamps can distribute PPFD more evenly .
For example, an LED lamp with a PPF of 1500 µmol/s has a PPFD of:
- 800 µmol/m²/s at a distance of 30 cm
- 500 µmol/m²/s at a distance of 60 cm
- 300 µmol/m²/s at a distance of 90 cm
💡 That's why light measurements at different heights are essential!
Conclusion: Why PPFD is important for grow lights
✅ Measures the actual light intensity that plants receive.
✅ Helps choose the right light distance and strength.
✅ Determines the optimal growing conditions for different crops.