Does light passed through two window screens get polarized?

[Bob8102]

If you take two window screens and hold them, say, a couple feet apart and look through both of them, you see what looks like interference patterns. These types of patterns can also be seen in transparent materials when polarized light is passed through them. More on stressed materials and polarized light: https://www.sciencedirect.com/topics/materials-science/photoelastic-stress-analysis. I am thinking that light passed through two window screens is polarized and that’s why you see the interference patterns. Am I right?

 

[Jonathan Scott]

If you mean the sort of screen that has fine mesh on it, the patterns are nothing to do with polarization. They are Moiré patterns (also known as Moiré fringes):
https://en.wikipedia.org/wiki/Moiré_pattern

 

[BvU]

a couple feet apart

No pattern when less than that ?

$\$

 

[berkeman]

Welcome to PF, Bob.

I am thinking that light passed through two window screens is polarized

As @Jonathan Scott says, you are seeing Moire patterns, not anything to do with the polarization of light.

One important skill as an inventor is to be able to quickly eliminate false leads and non-fruitful paths of exploration. That helps you to optimize the creative time and other work that you are putting into your ideas for inventions. In this case, there is an easy way for you to tell if the effect you are seeing has anything to do with polarization. Can you say what you think that quick-check might be?

 

[berkeman]

BTW, a Google Images search turns up lots of examples of Moire patterns:

 

[BillTre]

If it were polarized, you would be able to hold up polarized sunglasses to it and see a difference in brightness as you rotated the glasses.

 

[Bob8102]

I'm sure the patterns appear if the screens are closer apart than two feet. According to the above post, it is not polarized light but it is an interference pattern.

 

[hutchphd]

Just to be clear it is an interference pattern between the "wavelength" of the screens not of the light.
And just to muddy the water: a vernier scale actually uses a (usually 1D) Moire pattern.

 

[sophiecentaur]

Just to be clear it is an interference pattern between the "wavelength" of the screens not of the light.

This effect must have been noticed (between layers of fine cloth) but perhaps not identified and named long before diffraction / interference of light was noticed and explained.
The two effects seem to have been studied at much the same time. Here,
and Here are references to mid 17th Century work. There must have been a lot of thinking about the similarities and differences at the time.

There is additional possible confusion when you look at the patterns you can get when viewing single points of light through a single layer of fine woven cloth. (I still enjoy observing street lamps through the fabric of a rotating umbrella on a wet night.)