Calculator
Example data table
| Scenario | PPFD (µmol/m²/s) | Factor | Lux (approx) |
|---|---|---|---|
| Seedlings under cool white LED | 200 | 57 | 11,400 |
| Vegetative growth under white LED | 400 | 67 | 26,800 |
| Flowering under HPS | 600 | 82 | 49,200 |
| Outdoor bright daylight | 1200 | 54 | 64,800 |
Formula used
- Lux = PPFD × Conversion Factor
- Foot-candles = Lux ÷ 10.764
- DLI (optional) = PPFD × 3600 × hours ÷ 1,000,000
The conversion factor depends on the light spectrum and the meter’s response. Use a preset for quick estimates, or enter a custom factor for your fixture.
How to use this calculator
- Measure PPFD at canopy height using a quantum sensor.
- Select the light source preset closest to your fixture.
- Optionally enter photoperiod hours to estimate DLI.
- Click Calculate to see lux, fc, and DLI.
- Download CSV or PDF to save and share results.
Why PPFD and lux describe different things
PPFD counts plant‑useful photons from 400–700 nm, in µmol/m²/s. Lux reflects human brightness, weighted by eye response. Spectral shifts change lux at the same PPFD, so any factor is approximate. Always record the factor used. Use this tool to translate readings for daily reports and quick audits routinely.
Selecting a conversion factor with confidence
Start with a preset matching lamp type and color temperature. White LEDs vary because phosphors reshape output. HPS often reads higher lux per PPFD from yellow emission. Red‑blue fixtures can look dim in lux yet deliver strong PPFD. For best accuracy, measure lux and PPFD at the same point. Compute lux ÷ PPFD, and average across dimming settings. If you use a different meter later, recheck the factor, because sensors respond differently.
Turning lux targets into practical garden actions
Lux helps you spot uneven lighting fast. Take a grid of readings across the bench and compare edge values to the center. Raise or lower fixtures, add side reflection, or reposition plants to improve uniformity. When sharing goals with non‑specialists, report lux alongside PPFD. Include the distance and settings used. Saving these details makes repeat checks consistent.
Using DLI to balance intensity and time
DLI is the daily total of photosynthetic light in mol/m²/day. It links intensity and time, so lower PPFD can work with a longer photoperiod. Enter hours to estimate DLI, then compare schedules across seasons. More DLI is not always better; heat, CO₂, and nutrition can become limiting. Match targets to crop stage and adjust while watching color and posture.
Measurement tips that improve repeatability
Measure at canopy height with the sensor level. Avoid shading the sensor, and let fixtures warm up before recording. Take several points and use an average for decisions. Note distance, dimming, and any diffuser or lens changes. Keep sensor domes clean, and remember bright walls can raise readings. Repeat the method each time for trends.
FAQs
1) Is PPFD to lux conversion exact?
No. Lux depends on spectrum and sensor response, so the factor is an approximation. A custom factor measured for your fixture and meter will be closer.
2) Which preset should I choose for my LED grow light?
Pick the preset closest to your LED’s color temperature and type. If it is a mixed-spectrum grow bar, consider measuring a custom factor or start with the generic white LED value.
3) Why does my lux meter show high numbers under HPS?
HPS emits strong yellow light where human eyes are very sensitive. Lux weights that region heavily, so lux per PPFD often appears higher than under cooler spectra.
4) What is DLI and why does it matter?
DLI is the total photosynthetic light delivered per day. It helps compare different PPFD and photoperiod combinations, supporting consistent growth and energy planning.
5) Can I use lux alone to set lighting for plants?
Lux is helpful for uniformity checks and quick comparisons, but PPFD and DLI align better with plant response. Use lux with a suitable factor and keep PPFD measurements when possible.
6) How do I create a custom conversion factor?
Measure PPFD and lux at the same location and time. Divide lux by PPFD to get lux per µmol/m²/s. Repeat at several points and average the results.