Calculator
Example data table
| Scenario | Input | Assumptions | Estimated PPFD | DLI (18h) |
|---|---|---|---|---|
| Herbs, white LED | 18,000 lx | Factor 0.015, 0% extra loss | 270 µmol/m²/s | 17.5 mol/m²/day |
| Leafy greens, lumens | 24,000 lm over 1.2 m² | UF 0.85, MF 0.95, factor 0.015 | 242 µmol/m²/s | 15.7 mol/m²/day |
| Fruit crop, PPF | 700 µmol/s over 1.0 m² | Delivery 0.90, 10% extra loss | 567 µmol/m²/s | 36.7 mol/m²/day |
| Low-light seedlings | 8,500 lx | Factor 0.016, 0% extra loss | 136 µmol/m²/s | 8.8 mol/m²/day |
Formula used
- PPFD ≈ Lux × Factor
- Lux ≈ (Lumens × UF × MF) ÷ Area
- PPFD ≈ (PPF × Delivery) ÷ Area
- PPFD_effective = PPFD_raw × (1 − Loss%)
How to use this calculator
- Pick the method that matches your available data.
- Choose a spectrum preset, or enter a custom factor.
- For lumens or PPF, enter the grow area accurately.
- Add realistic loss and uniformity values for your setup.
- Set photoperiod to get DLI for crop planning.
- Calculate, then download a report for recordkeeping.
What PPFD tells you at canopy level
PPFD estimates how many photons reach your leaves directly. Values are shown in µmol/m²/s, making comparisons consistent across fixtures. Many herbs and leafy greens respond well around 200–450, while fruiting crops often need 400–700+ when nutrition and temperature are aligned. Use the uniformity field to see how an “average” reading can hide weak corners.
Choosing the right input method
Use Lux when you measure light with a phone meter or inexpensive sensor, but treat it as a spectrum-dependent estimate. Use Lumens when you have fixture lumen output and a defined grow area; utilization and maintenance factors help convert “rated” lumens into canopy lux. Use PPF when you have lab specs in µmol/s; it usually delivers the most stable prediction because it already targets plant-effective wavelengths.
Spectrum factor and why it changes
The lux-to-PPFD factor converts human-vision units into plant-vision units. White LEDs often cluster near 0.014–0.016, while HPS can be lower. Two lights with the same lux can produce different PPFD because their spectra weight the lux sensor differently. If you own a PAR meter, take a paired lux and PPFD reading once and store the custom factor for repeatable results.
Losses, uniformity, and practical layout checks
Real canopies lose photons to distance, reflectors, tent walls, and leaf angle. The additional loss percentage lets you apply a conservative correction after your raw calculation. Uniformity (min/avg) supports quick layout checks: a value of 0.70 suggests corners may run near 70% of the average, while the brightest spots may run about 1/0.70 of the average.
Turning PPFD into DLI for crop planning
DLI converts intensity into a daily total using your photoperiod. For example, 300 PPFD for 18 hours is about 19.4 mol/m²/day. This helps you compare short, intense schedules to longer, gentle ones and align targets with crop stage. Recalculate after dimming, raising fixtures, or changing reflectivity so your DLI stays consistent.
FAQs
Is lux a reliable way to estimate PPFD?
Lux can work for quick checks, but accuracy depends on spectrum and the sensor. Use an appropriate preset or a custom factor, and validate at least once with a PAR meter if precision matters.
Why does the same PPFD give different results in different corners?
Fixtures rarely distribute photons evenly. Height, optics, reflectivity, and obstructions create hot spots and dim zones. The uniformity setting helps estimate that spread so you can reposition lights or add reflectors.
Which method should I prefer: lux, lumens, or PPF?
Prefer PPF when you have fixture lab data in µmol/s. Use lumens when you know true lumens and your grow area. Use lux when you only have readings and accept a spectrum-based approximation.
What utilization and maintenance factors should I use?
Start with utilization 0.80–0.90 for reflective enclosures and 0.60–0.80 for open rooms. Use maintenance 0.90–0.98 depending on lens cleanliness and fixture age. Adjust after comparing to real measurements.
How do I pick a photoperiod for DLI?
Choose a schedule your crop tolerates and your environment can support. Many seedlings use 16–18 hours, leafy greens 14–18, and fruiting crops 12–18 depending on variety. Use DLI to hit your daily target.
What is a good custom lux-to-PPFD factor?
Take one paired measurement: record lux and PPFD at the same spot and height. Divide PPFD by lux to get your factor. Repeat in a few locations and average the ratios for a stable calibration.