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QUESTION: How do polarized sunglasses lens work? I purchased sunglasses  which are apparently polarized and my led display of my car radio has a dark streak diagonally down the middle of the display and the streak moves when I tilt my head. What would cause something simple like a led display to emit light in particular direct so polarized lens would see parts of it intermittently? I would think it would project light in many directions equally so polar lens would not show it any differently?

ANSWER: Polarized lenses are designed to reduce glare by preferentially filtering out light which is polarized parallel to the ground.  Since scattered light picks up a degree of polarization in this way, the technique is very effective.  Unpolarized sunglasses are just dark lenses.

By LED display, do you mean actual individual LEDs or a flat liquid crystal display?  There are a few schemes, but they generally all involved light which is polarized.  LEDs are not polarized, in general.  The direction of polarization depends on the design scheme, but there's no reason it has to be uniform across your entire display.  If the light that comes through the display is polarized in a way that your sunglasses will block, it will be blocked.  With LCD displays, this can result in a wide variety of odd-looking results.  The display may emit light pretty evenly, but the angle of polarization is something your eye is not equipped to determine.   So this display was not designed with polarized lenses in mind.  Other examples of such displays can be found all over, in calculators and computers.

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QUESTION: I don't know in what form leds come in these days and can't confirm if it is polarized or not but later when it is darker I could attemp lt a photo to show you?

ANSWER: Sure, you can add photos on these questions here.  A camera should respond through your lenses roughly the same as your eyes.  Even if you just take a picture of the screen, the photo will let me know if it's an LCD type screen...but I'm betting it is.  If it's a screen with messages and such, it's a liquid crystal display (LCD) screen.  If it's individual lights forming patterns, it might be an LED display.

Also, though it will darken the display, a cheap piece of polarizing plastic on the screen at an angle (google it) will rotate the polarization of light.  That, or non-polarized sunglasses would help your problem seeing the display.

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QUESTION: Scratch that. I wasn't able to get a good picture at night. Slight dark band but it doesn't move with glasses moving like during the day. Maybe it is a plastic film on display.

Wondering. Do some colors or like materials polarize certain ways? Like a way to hide a message in plain site?

It could be glare from the display.  Lots of weird stuff happens with polarized lenses.  Light can pick up polarization by passing through glass, through those sunglasses you've probably noticed that some glass has weird patterns.  It could pick up polarization from reflection off of the display, or through it.  But there's no message there unless you write one.  Yes, that is possible to do, make a message you could only see with polarized lenses, but probably not worth your time.  It's how they can project two images on the same screen in a 3D movie, but your eyes can only see one each (creating the 3D effect) through the special glasses.


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Dr. Stephen O. Nelson


I can answer most basic physics questions, physics questions about science fiction and everyday observations of physics, etc. I'm also usually good for science fair advice (I'm the regional science fair director). I do not answer homework problems. I will occasionally point out where a homework solution went wrong, though. I'm usually good at explaining odd observations that seem counterintuitive, energy science, nuclear physics, nuclear astrophysics, and alternative theories of physics are my specialties.


I was a physics professor at the University of Texas of the Permian Basin, research in nuclear technology and nuclear astrophysics. My travelling science show saw over 20,000 students of all ages. I taught physics, nuclear chemistry, radiation safety, vacuum technology, and answer tons of questions as I tour schools encouraging students to consider careers in science. I moved on to a non-academic job with more research just recently.

Ph. D. from Duke University in physics, research in nuclear astrophysics reactions, gamma-ray astronomy technology, and advanced nuclear reactors.

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