PhotoCalcs
Light Meter Calculator — Lux, Foot-candles & EV Conversion
Convert between lux, foot-candles and Exposure Value for light metering and studio work.
How We Calculate This
This calculator converts between common light measurement units used in photography:
- Lux to EV: EV = log₂(Lux ÷ 2.5) — incident light relationship at ISO 100
- EV to Lux: Lux = 2.5 × 2^EV — reverse calculation
- Foot-candles to Lux: 1 fc = 10.764 lux
- Lux to Foot-candles: 1 lux = 0.0929 fc
The calibration constant 2.5 is the standard value used in incident light meters (Sekonic, etc.). Reflected meters use a different constant.
Frequently Asked Questions
Lux is the SI unit of illuminance, measuring how much luminous flux falls on a surface. One lux equals one lumen per square metre. Bright sunlight is about 100,000 lux, an overcast day 1,000-10,000 lux, and a well-lit office 300-500 lux.
For incident light metering, EV = log2(Lux / 2.5). This uses a calibration constant of 2.5, which is standard for incident meters. The relationship assumes ISO 100. For different ISO values, add log2(ISO/100) to the EV.
A foot-candle (fc) is an imperial unit of illuminance equal to one lumen per square foot. 1 foot-candle = 10.764 lux. It is still commonly used in the US film and TV industry for lighting specifications.
Bright sun: EV 14-16. Overcast: EV 12-13. Indoor daylight: EV 8-10. Well-lit room: EV 7-8. Dim interior: EV 4-6. Candle light: EV 1-2. Full moonlight: EV -2 to -3.
Related Calculators
EV Calculator
Calculate Exposure Value from your camera settings or convert between EV, lux and foot-candles. Ideal for matching light meter readings. Free calculator.
Sunny 16 Calculator
Estimate correct exposure settings using the Sunny 16 rule for outdoor photography. Select lighting conditions for instant aperture and shutter recommendations.
Flash Exposure Calculator
Calculate flash power from guide number, subject distance and aperture. Work out the correct flash-to-subject settings for any strobe. Free calculator.
Zone System Calculator
Map scene luminance values to Ansel Adams Zone System zones from 0 to X. Visualise tonal placement for precise black-and-white exposure control.
Exposure Triangle Calculator
Balance aperture, shutter speed and ISO to achieve correct exposure. Adjust one setting and see how the others compensate. Free online calculator.
Was this calculator helpful?
Last updated: February 2026
All calculations are estimates based on standard optical and photographic formulas. Results may vary with specific equipment.