Estimate lux or traditional 400–700 nm PPFD using a spectrum-specific or custom factor. Optional photoperiod gives constant-output DLI; the factor-sensitivity band is an illustrative range, not a confidence interval.
Lux To PPFD Formula
The following estimates traditional 400–700 nm PPFD from illuminance using a factor appropriate to the light spectrum.
Variables:
- PPFD is the Photosynthetic Photon Flux Density (μmol/m²/s)
- Lux is illuminance (lm/m²), weighted for human photopic vision
- CF is the spectrum-dependent factor in (μmol/m²/s) per lux; the sunlight preset is approximately 0.0185
Estimate PPFD = lux × CF, or invert the same factor with lux = PPFD / CF. Apogee’s source-specific table lists sunlight 0.0185, cool-white fluorescent 0.0135, mogul-base HPS 0.0122 and metal halide 0.0141. These approximate factors do not describe every lamp in a category. The calculator’s white LED factor 0.0146 is an illustrative retained assumption; use a measured or spectrum-derived custom factor when available. A lux conversion estimates PPFD and does not independently verify plant-growth suitability or measurement accuracy.
| Lux (lx) | PPFD (μmol/m²/s) | Foot-candle (fc) |
|---|---|---|
| 100 | 1.50 | 9.29 |
| 200 | 3.00 | 18.58 |
| 300 | 4.50 | 27.87 |
| 500 | 7.50 | 46.45 |
| 750 | 11.25 | 69.68 |
| 1000 | 15.00 | 92.90 |
| 1500 | 22.50 | 139.35 |
| 2000 | 30.00 | 185.81 |
| 3000 | 45.00 | 278.71 |
| 5000 | 75.00 | 464.52 |
| 7500 | 112.50 | 696.77 |
| 10000 | 150.00 | 929.03 |
| 15000 | 225.00 | 1393.55 |
| 20000 | 300.00 | 1858.06 |
| 30000 | 450.00 | 2787.09 |
| 40000 | 600.00 | 3716.12 |
| 50000 | 750.00 | 4645.15 |
| 60000 | 900.00 | 5574.18 |
| 80000 | 1200.00 | 7432.24 |
| 100000 | 1500.00 | 9290.30 |
| Illustrative custom-factor example: PPFD ≈ lux × 0.015. These rows use a different factor from the calculator’s 0.0146 white LED assumption. No universal factor applies to all spectra. 1 foot-candle (fc) ≈ 10.7639104 lux (lx). | ||
What Does “Lux to PPFD” Mean?
Lux measures incident luminous flux per area with human visual weighting. Traditional PPFD counts incident photons from 400 to 700 nm equally, in μmol/m²/s. Their ratio depends on the spectral distribution, so lux alone cannot uniquely determine PPFD. A suitable quantum sensor measures PPFD directly; a lux-based estimate cannot establish crop response, an optimal lighting level or the effects of photons outside this traditional band.
How to Calculate Lux To PPFD?
The following steps outline how to calculate the Lux To PPFD using the formula: PPFD = Lux * CF.
- Measure illuminance in lux at the position and plane of interest, or select the inverse mode and enter PPFD.
- Select a matching approximate spectrum factor or enter a positive custom CF in (μmol/m²/s) per lux.
- Use PPFD ≈ lux × CF, or lux ≈ PPFD / CF. Both directions use the same selected factor.
- Optionally enter 0–24 hours of constant light output. DLI = PPFD × hours × 3600 / 1,000,000, in mol/m²/day. Changing daylight requires integration over the day.
- Optionally vary CF by ±10%, ±15% or ±20%. PPFD endpoints are lux × CF × (1 ± b); inverse lux endpoints are PPFD/[CF(1 + b)] and PPFD/[CF(1 − b)]. This is sensitivity to an assumed factor variation, not a statistical confidence interval.
Example Problem:
Use the following variables as an example problem to test your knowledge.
Lux = 500
CF = 0.0185 (sunlight assumption). Estimated PPFD = 500 × 0.0185 = 9.25 μmol/m²/s. If that PPFD remains constant for 12 hours, DLI = 9.25 × 12 × 3600 / 1,000,000 = 0.3996 mol/m²/day.
