# Polarized lens sunglasses and car window 'spots'

**URL:** <https://boards.straightdope.com/t/polarized-lens-sunglasses-and-car-window-spots/56942>\
**Category:** Factual Questions\
**Created:** [March 6, 2001, 3:53pm UTC](https://boards.straightdope.com/t/polarized-lens-sunglasses-and-car-window-spots/56942 "2001-03-06T15:53:04Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![Myndephuquer](https://avatars.discourse-cdn.com/v4/letter/m/f0a364/32.png) [@Myndephuquer](https://boards.straightdope.com/u/Myndephuquer)\
**Post date:** [March 6, 2001, 3:53pm UTC](https://boards.straightdope.com/t/polarized-lens-sunglasses-and-car-window-spots/56942/1 "2001-03-06T15:53:04Z")

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What are those ‘spots’ that I see on car windows when I’m wearing my polarized-lens sunglasses?

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**Author:** ![Great\_Dave](https://avatars.discourse-cdn.com/v4/letter/g/46a35a/32.png) [@Great\_Dave](https://boards.straightdope.com/u/Great_Dave)\
**Post date:** [March 6, 2001, 5:24pm UTC](https://boards.straightdope.com/t/polarized-lens-sunglasses-and-car-window-spots/56942/2 "2001-03-06T17:24:42Z")

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Automotive safety glass is stretched in such a way as to make it break into little bits. Those spots are a result of that. Usually, the molecules in glass are randomly oriented, so no polarization effect occurs. The stretching changes that.

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**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\
**Post date:** [March 6, 2001, 5:44pm UTC](https://boards.straightdope.com/t/polarized-lens-sunglasses-and-car-window-spots/56942/3 "2001-03-06T17:44:34Z")

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We had this same question a few months ago, with more answers. I’ll search up the link once board is moving at reasonable speed again.

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**Author:** ![Myndephuquer](https://avatars.discourse-cdn.com/v4/letter/m/f0a364/32.png) [@Myndephuquer](https://boards.straightdope.com/u/Myndephuquer)\
**Post date:** [March 6, 2001, 7:38pm UTC](https://boards.straightdope.com/t/polarized-lens-sunglasses-and-car-window-spots/56942/4 "2001-03-06T19:38:03Z")

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BigDaddyD – Thanks for the response. It doesn’t quite explain the checkerboard effect that I see, but it’s a start.

Chronos – I searched the SDMB and the column archive and didn’t come up with anything. A link would be appreciated. Did that thread or column also explain why Pontiac minivan windshields look metallic purple through polarized lens?

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**Author:** ![Mr.Cynical](https://avatars.discourse-cdn.com/v4/letter/m/ee59a6/32.png) [@Mr.Cynical](https://boards.straightdope.com/u/Mr.Cynical)\
**Post date:** [March 6, 2001, 7:58pm UTC](https://boards.straightdope.com/t/polarized-lens-sunglasses-and-car-window-spots/56942/5 "2001-03-06T19:58:50Z")

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If Chronos doesn’t beat me there:

You’ve got this thread:  
[http://boards.straightdope.com/sdmb/showthread.php?threadid=36870](http://boards.straightdope.com/sdmb/showthread.php?threadid=36870)

Which, in turn, links to this thread:  
[http://boards.straightdope.com/sdmb/showthread.php?threadid=28782](http://boards.straightdope.com/sdmb/showthread.php?threadid=28782)

(and I threw this one in for good measure: )  
[http://boards.straightdope.com/sdmb/showthread.php?threadid=12439](http://boards.straightdope.com/sdmb/showthread.php?threadid=12439)