How do I measure illuminance (lux or foot-candles)?

The easiest way is to convert EV (exposure values to Lux and then Lux to ft. candles.

The Lux unit is metric whereas the ft. candle is English. Only the United States and Liberia are retaining the English system.

Your light meter will provide the data on exposure in EV (exposure) values. It is easy to convert EV to Lux.

The formula is (2^Lx) * 2.5

An exit (thanks for the input) --- Converting EV to Lux: While the two values are different, an incident light meter reading can be approximately converting using the formula 2.5 x 2^EV

Example --- If the EV reading is 6, what is the scene brilliance in Lx? Answer : 2^6 = 64 X 2.5 = 160 Lx

Once we know scene brilliance in Lx, we can easily convert to ft. candles. The formula Lx X 0.0929

Convert 160 Lx to ft. candles 160 X 0.0929 = 14.86 ft. Candles.

Table to convert EV to Lx and ft. candles

EV LUX ft. candles 1 EV 5.00 Lx 0.46 ft. candles

2 EV 10.00 Lx 0.93 ft. candles

3 EV 20.00 Lx 1.86 ft. candles 4 EV 40.00 Lx 3.72 ft. candles

5 EV 80.00 Lx 7.43 ft. candles

6 EV 160.00 Lx 14.86 ft. candles

7 EV 320.00 Lx 29.73 ft. candles

8 EV 640.00 Lx 59.46 ft. candles

9 EV 1,280.00 Lx 118.92 ft. candles

10 EV 2,560.00 Lx 237.83 ft. candles

11 EV 5,120.00 Lx 475.66 ft. candles

12 EV 10,240.00 Lx 951.33 ft. candles

13 EV 20,480.00 Lx 1,902.65 ft. candles

14 EV 40,960.00 Lx 3,805.31 ft. candles

15 EV 81,920.00 Lx 7,610.61 ft. candles

16 EV 163,840.00 Lx 15,221.23 ft. candles

17 EV 327,680.00 Lx 30,442.46 ft. candles

18 EV 655,360.00 Lx 60,884.91 ft. candles