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.

How do I convert lux to EV?

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.

What is a foot-candle?

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.

What EV do I need for different scenes?

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.

PhotoCalcs

Light Meter Calculator — Lux, Foot-candles & EV Conversion

Convert between lux, foot-candles and Exposure Value for light metering and studio work.

Conversion Mode

Illuminance (Lux)

How We Calculate This

This calculator converts between common light measurement units used in photography:

Lux to EV: EV = log&sub2;(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.

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Last updated: February 2026

All calculations are estimates based on standard optical and photographic formulas. Results may vary with specific equipment.