How can I measure illuminance in lux or foot-candles with a Luna Pro light meter?
Asked 11/10/2020
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2 answers
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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
2
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
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:
- Take an incident reading with the Luna Pro
- Note the EV value
- Compute lux from EV
- 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.
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