Light is the decisive factor for abundant cannabis yields – but the world of light measurement can be confusing. In this guide, I’ll explain exactly how to use PAR, PPFD & Co. to provide your plants with the best possible care.
1st PAR: Not every light counts!
Photosynthetically active radiation (PAR, 400-700 nm) is the only range that your plants use for photosynthesis.
Attention, myth!
❌ “More PAR = automatically better growth”
✅ Truth: PAR says nothing about light quality or distribution. UV/infrared (outside of PAR) influence trichome formation, for example!
2nd PPFD: Your secret for thick buds
PPFD (µmol/m²/s) measures how many “photosynthetic particles” actually reach your leaves.
Optimal values for cannabis (H3)
| Growth phase | Ideal-PPFD |
|---|---|
| Seedling | 200-400 |
| Vegetation | 400-600 |
| blossom | 600-900 |
⚠️ Mistakes you must avoid:
- Too close to the lamp (>1000 PPFD) → Burnt leaves
- Too far away (<300 PPFD) → Asparagus shoots
3. lumen & foot-candle – why they deceive you
- Lumen: Measures brightness for humans (e.g. 800 lumen lamp).
- Foot-candle: Obsolete unit (1 FC = 10.76 lux).
💡 Note: These values say nothing about plant growth! A “bright” lamp can be useless if it does not emit PAR light.
Conclusion: Not all light is the same!
- Measure PAR/PPFD → Buy an inexpensive PAR meter (from €50).
- Ignore lumens – only relevant for living room lamps.