How to use it
- Choose EV to lux, or lux to EV.
- Enter the value. Leave the meter constant at 250 unless your meter says otherwise.
- Read the illuminance in lux and foot-candles, or the EV at ISO 100.
How it works
With ISO 100, lux = C × 2^EV ÷ 100 (with C = 250: 2.5 × 2^EV), and the inverse is EV = log2(lux × 100 ÷ C). Foot-candles are lux ÷ 10.7639. The constant is a calibration choice by meter makers, so results can differ by tens of percent between meters; they are not a substitute for a calibrated measurement.
Worked example
EV 15 with C = 250: 2.5 × 32,768 = 81,920 lux, roughly bright direct sunlight. Going the other way, 100 lux gives log2(100 × 100 ÷ 250) = log2(40) ≈ 5.32 EV.
Tips
- Every EV step doubles the illuminance.
- Use the exposure value calculator to turn camera settings into an EV first.