# Least expensive method of reliably measuring moonlight?



## metroplex (May 4, 2007)

Are there any light meters that can read very low light (moonlight) and don't cost a lot of money? This isn't for photography and ideally I want something that I can press a button and tell me the amount of ambient lighting under very low light conditions. Thanks in advance.


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## SilverFox (May 5, 2007)

Hello Metroplex,

Welcome to CPF.

In the wilderness, the amount of light from an overcast night sky is reported to be in the 0.0001 lux range. Most light meters will not measure down that low. However, a full moon gives around 0.1 lux, and most light meters will measure that without problems. I have an Extech EA30 that reads 0.01 lux, but it is not sensitive enough for very low light measurements.

Tom


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## metroplex (May 5, 2007)

Hi SilverFox,

That makes a lot of sense. I did some calculations using an EV of -6 and the amount of foot-candles/lux is truly small compared to the 0.01 Lux resolution of most meters.

Is there anything I could do (at a reasonable cost) to take ambient measurements in low light conditions?


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## greenlight (May 5, 2007)

are you looking for actual readings or just a comparitive test?


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## SilverFox (May 6, 2007)

Hello Metroplex,

Low light measurement can be difficult. You may be able to use the Sky Quality Meter to get a measurement, then, I believe, they have a conversion factor that may make the reading more useful.

Tom


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## 2xTrinity (May 7, 2007)

You might consider using a big focusing lens (such as a Fresnel lens) or a parabolic reflector of known magnification to amplify the moonlight to a level readable by a common light meter. You could even calibrate it by taking a light source that is readable, such as an LED, and measuring the lux without the amplification, then, measure how much it increases by adding the lens/reflector, and use that perecentage change as a conversion factor.


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