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I have a piece of either circular or linear polarized film that I had laying around, however, I have no knowledge of the degree of polarization that the film has. How can I test to see what the degree of polarization is. I have my monitor and other screens to test it against but again I do not know the polarization degree of the monitor either. Can someone help?

ForeverLearningJP
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  • you got 1 piece or 2? – JEB May 23 '19 at 02:33
  • I've got many pieces that I can retrieve, one being most likely at 45 degrees of polarization. If I place a piece of this 45 degree polarizer over my TV, I have to tilt it to 45 degrees to fully block light, does this mean that my TV screen has 0 degrees of polarization? – ForeverLearningJP May 23 '19 at 14:44
  • What do you mean by "degree" of polarization? – JEB May 23 '19 at 17:28
  • @JEB, If I go to find a piece of polarized film, the polarized film is polarized at a certain angle to align with the crystal structure of whichever LCD display. Typically they would polarize the film at 0 degrees, 45 degrees, 90 degrees. Id like to know, that in the instance I have a piece from a recycled product, how will I know what angle it was polarized at? – ForeverLearningJP May 23 '19 at 22:51
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    Linear polarization isn't a vector, it's a tensor alignment. That is, it doesn't have a direction, it has an alignment, and is unchanged by a 180 degree rotation (as opposed to 360 for a vector). But you edited the question to "circular" polarizer, which is "right" or "left" handed, and doesn't have an angle at all. – JEB May 25 '19 at 00:11
  • Observe the reflected light from a mirror. – Samyak Marathe Sep 08 '22 at 11:45

3 Answers3

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Surely you need second polarizer with known properties.

In the lab we can surely use something fancy like Glan–Taylor prism, but it is not required. The easiest way is to use a piece of flat glass rotated to Brewster angle as a polarizer. For regular glass Brewster angle is ~56.62°.

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Please keep in mind, that many linear polarizers for photography convert linear light to circular polarization after the filter (so that it does not interfere with DSLR cameras focusing system - much less important with mirrorless).

BarsMonster
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I may be wrong but find a flat level shiny surface like a glass table top and stand where you can see a good strong reflection. Down low where the angle of reflection is wide is better. The photons coming at you should be polarized mostly horizontally. Look through the polarizer at the reflection and slowly rotate it. It should get darker when the polarizer is vertical and brighter when the polarizer is horizontal.

Bill Alsept
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  • A car windshield will work find for this, or the surface of a pond, even the blue sky is polarized. – JEB May 25 '19 at 00:03
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You could use haidingers brushes to see the polarization of your LCD with your eyes and then use that to find the polarisation of your filter.

Azzinoth
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