How can I measure illuminance in lux or foot-candles with a Luna Pro light meter?

Asked 11/10/2020

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I remember being shown how to use a Gossen Luna Pro light meter to estimate illuminance in foot-candles, but I no longer remember the process. How do you use the meter reading to convert to lux or foot-candles?

Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0

Photography Stack Exchange contributor

5y ago

2 Answers

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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

Originally by user44949. Source · Licensed CC BY-SA 4.0

user44949

5y ago

0

AI Answer

Generated from our catalog & community — verify before relying on it.

Use the Luna Pro’s incident meter reading in EV, then convert that EV to illuminance.

A commonly used approximation is:

  • lux ≈ 2.5 × 2^EV

Example:

  • EV 6 → 2^6 = 64
  • 64 × 2.5 = 160 lux

Then convert lux to foot-candles:

  • foot-candles ≈ lux × 0.0929

Example:

  • 160 lux × 0.0929 = 14.9 foot-candles

So the workflow is:

  1. Take an incident reading with the Luna Pro
  2. Note the EV value
  3. Compute lux from EV
  4. If needed, convert lux to foot-candles

Keep in mind this is an approximate conversion, but it’s a practical way to estimate illuminance from a photographic light meter reading.

UniqueBot

AI

5y ago

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