Polarizing filter to bring lux down?

bstrickler

Enlightened
Joined
Jul 13, 2008
Messages
831
Location
Tucson, Arizona
I was just reading a light build where the persons light overloaded their luxmeter (20k lux meter), resulting in an unknown output.

I was wondering if it would be logical to use a rotating polarizing filter to bring the light down to a level that the meter can read, and extrapolate the true lux by using a light with a known lux at said distance, and if the lower light is brought down by 1500 lux, that would mean the light that overloads the luxmeter is 1500 lux higher than what it says without the polarizing filter.

Does that make sense?

I guess the simpler way to test the method would be to get a few lights over say 10k lux at set distance, then put a rotating (adjustable darkness) polarizing filter in front of the light, and see if that setting brings all the lights down by the same amount +-100 lux. If it does, I would think that you could use a polarizing filter to calculate the actual output of the light. At that point, you could invest in a set of polarized filters with amounts like 10%, 20%, 30%, etc, so you know that if you use a 20% filter on said light, you know it blocks out 20% of the light, which means the reading ends up being X lux (i.e. reads 19klux with the filter, which would result in a real output of ~23,750 lux).

Just wondering if that actually works. If I had a luxmeter, I'd be more than willing to try that.
 

AnAppleSnail

Flashlight Enthusiast
Joined
Aug 21, 2009
Messages
4,200
Location
South Hill, VA
I was just reading a light build where the persons light overloaded their luxmeter (20k lux meter), resulting in an unknown output.

I was wondering if it would be logical to use a rotating polarizing filter to bring the light down to a level that the meter can read, and extrapolate the true lux by using a light with a known lux at said distance, and if the lower light is brought down by 1500 lux, that would mean the light that overloads the luxmeter is 1500 lux higher than what it says without the polarizing filter.

Does that make sense?

I guess the simpler way to test the method would be to get a few lights over say 10k lux at set distance, then put a rotating (adjustable darkness) polarizing filter in front of the light, and see if that setting brings all the lights down by the same amount +-100 lux. If it does, I would think that you could use a polarizing filter to calculate the actual output of the light. At that point, you could invest in a set of polarized filters with amounts like 10%, 20%, 30%, etc, so you know that if you use a 20% filter on said light, you know it blocks out 20% of the light, which means the reading ends up being X lux (i.e. reads 19klux with the filter, which would result in a real output of ~23,750 lux).

Just wondering if that actually works. If I had a luxmeter, I'd be more than willing to try that.

In theory the math is easier if you walk away slowly. Double the distance and you cut the reading by 1/4. Distance is free, calibrated filters aren't.
 
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