# Polarized sunglasses vs. iPod Touch display?

**URL:** <https://boards.straightdope.com/t/polarized-sunglasses-vs-ipod-touch-display/547227>\
**Category:** Factual Questions\
**Created:** [July 19, 2010, 2:47pm UTC](https://boards.straightdope.com/t/polarized-sunglasses-vs-ipod-touch-display/547227 "2010-07-19T14:47:39Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\
**Post date:** [July 19, 2010, 2:47pm UTC](https://boards.straightdope.com/t/polarized-sunglasses-vs-ipod-touch-display/547227/1 "2010-07-19T14:47:39Z")

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If you’ve ever worn polarized sunglasses, then you probably know that they affect the viewing of standard LCD displays (which also make use of polarization): the LCD display may appear pitch black or completely normal depending on the angle to which you tilt your head.

Not so with my iPod Touch, and also (as I recently discovered) my local bank’s ATM display, and my cell phone. The colors are _slightly_ rotation-dependent, but not in the all-or-nothing way that “ordinary” LCD’s are (e.g. the odometer in my car, an '03 Maxima).

What is the display technology being used in these devices, and how is it that they are only slightly sensitive to polarization?

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**Author:** ![Turek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/turek/32/18782_2.png) [@Turek](https://boards.straightdope.com/u/Turek)\
**Post date:** [July 19, 2010, 4:27pm UTC](https://boards.straightdope.com/t/polarized-sunglasses-vs-ipod-touch-display/547227/2 "2010-07-19T16:27:31Z")

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I wear polarized sunglasses when I ride my motorcycle during the day, and I have a cheap LCD watch strapped to my handlebars. When I have my helmet visor up, I can’t read the watch; the display is pitch black. When I put my visor down, I can read it.

My theory is that the helmet visor depolarizes (scatters?) the light coming off the watch. Perhaps there’s something similar going on with the iPad? Something between the LCD and you depolarizing the light?

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<div class="post-metadata">

**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\
**Post date:** [July 19, 2010, 5:48pm UTC](https://boards.straightdope.com/t/polarized-sunglasses-vs-ipod-touch-display/547227/3 "2010-07-19T17:48:02Z")

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> [@Turek](#):
>
> I wear polarized sunglasses when I ride my motorcycle during the day, and I have a cheap LCD watch strapped to my handlebars. When I have my helmet visor up, I can’t read the watch; the display is pitch black. When I put my visor down, I can read it.
> 
> My theory is that the helmet visor depolarizes (scatters?) the light coming off the watch. Perhaps there’s something similar going on with the iPad? Something between the LCD and you depolarizing the light?

Hmmm, you may be on to something:

> **[Depolarizer (optics)](https://en.wikipedia.org/wiki/Depolarizer_(optics))**
>
> A depolarizer or depolariser is an optical device used to scramble the polarization of light. An ideal depolarizer would output randomly polarized light whatever its input, but all practical depolarizers produce pseudo-random output polarization.
> Optical systems are often sensitive to the polarization of light reaching them (for example grating-based spectrometers). Unwanted polarization of the input to such a system may cause errors in the system's output.
> The Cornu depolarizer was one of th...