UNIT CONVERSION
Convert lux and foot-candles
Use this conversion to compare readings written in different units. Conversion changes the unit, not the reliability or biological meaning of the measurement.
1 foot-candle = 10.7639 lux. Lux = foot-candles × 10.7639; foot-candles = lux ÷ 10.7639.
Example light bands
University extension charts use ranges that differ. The University of Maryland Extension groups low light as 25–100 fc, medium-bright as 100–500 fc, high as 500–1,000 fc, and direct indoor sunlight as above 1,000 fc. Another extension guide uses different cutoffs. Treat these as broad teaching categories, not precise plant requirements.
Lux bands shown here are unit conversions of those foot-candle values. They are not separate horticultural thresholds.
- 25–100 fc ≈ 269–1,076 lx
- 100–500 fc ≈ 1,076–5,382 lx
- 500–1,000 fc ≈ 5,382–10,764 lx
- Above 1,000 fc ≈ above 10,764 lx
What the conversion does not tell you
Lux is weighted for human vision, so it does not describe the amount or spectrum of light available for photosynthesis. A single reading also omits how long the plant receives light. Phone-meter apps can vary across devices and may be poorly calibrated. Use the houseplant measuring guide for a repeatable method and limitations.