How much light do plants need? (PPFD explained)
How much light does a plant need to grow and flower optimally? This is determined by the PPFD (Photosynthetic Photon Flux Density) value. In this article, we simply explain what PPFD is and how much light your plants need per growth phase.
🌱 What is PPFD?
PPFD stands for Photosynthetic Photon Flux Density and indicates how much light (photons) actually falls on the plant's leaf. This value is expressed in µmol/m²/s.
👉 The higher the PPFD, the more light is available for photosynthesis.
👉 PPFD is more important than lumens or watts, because it specifically concerns light that plants can use.
🔦 How much PPFD do plants need?
The ideal amount of light differs per growth phase:
| Phase | Recommended PPFD | Effect |
|---|---|---|
| Seedlings / cuttings | 100 – 300 µmol/m²/s | Gentle start, prevents stress |
| Growth phase | 300 – 600 µmol/m²/s | Rapid vegetative growth |
| Flowering phase | 600 – 1000+ µmol/m²/s | Maximum yield |
👉 Too little light inhibits growth, while too much light can cause damage.
📏 Distance between lamp and plant
The correct distance between grow light and plant determines the PPFD:
- Closer to the plant = higher PPFD
- Further from the plant = lower PPFD
👉 LED grow lights can often hang closer to the crop than HPS lamps, because they emit less heat.
⚡ PPFD vs Watt: what's the difference?
Many growers still look at Watt, but this only says something about energy consumption — not about usable light for plants.
- Watt: energy consumption
- PPFD: usable light for plants
👉 Modern LED grow lights deliver more PPFD per Watt and are therefore more efficient.
👉 Choose the right grow light directly?
View our LED grow lights with high PPFD.
🌿 Practical tips
- Use a dimmable LED lamp to regulate PPFD
- Start low with young plants and gradually build up
- Watch for signs of stress (pale leaves or burning)
- Ensure even light distribution
🔗 Learn more about light?
Do you want to delve deeper into light and plant growth?
✅ Conclusion
- PPFD determines how much usable light plants receive
- Each growth phase has a different light requirement
- LED grow lights offer the best control over PPFD
- The right balance ensures healthy growth and maximum yield