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Back story: At work we deal with confidential data, however our desk layout does not allow for screen privacy. We do not a privacy screens and are not allowed to take apart our screens.

In searching I found this question: What happens if you remove the polarization filter from a computer monitor?

Summary: You can take apart the screen and remove the polarizing layer, and then wear polarized shades or something to see the screens contents.

As mentioned above, I can not take apart the work LCD-TFT screen. But it would it be possible to add (tape) a polarized layer (from home) on top.

Question: Would adding a new polarizing layer on-top of an unmodified screen to make it invisible to the naked eye?


From my vary limited understanding (googling) of physics and LCDs I am thinking the light would be re-twisted by the additional layer. I apologize in advance I know little about physics so please keep it basic. I would like to know yes/no and the scientific reason why.

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    $\begingroup$ I believe there are simple film-like products that can be attached over any polarized screen that decreases the effective viewing angle of any polarized screen. I believe they attach just by a weak adhesive similar to a sticky note and can be easily removed without damaging the screen. I do not recall what these are called, but a few colleagues of mine that work for ATK have them. $\endgroup$ Apr 13, 2016 at 16:46
  • $\begingroup$ @honeste_vivere Thank you, I have found some on amazon, I may go this route if I do not have other options. However because of the office setup I have clients standing directly behind me so this is not fully optimal. $\endgroup$
    – Gram
    Apr 13, 2016 at 18:12
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    $\begingroup$ What is your real problem? It seems you want to avoid "clients standing directly behind you" seeing the screen. This seems like a business problem. If the business finds it acceptable, them you shouldn't sweat the problems caused by the business practice. If this isn't acceptable to the business then the business needs to provide you desk space such that customers are forced to stand in front of the desk in such a way that they can't see your screen. $\endgroup$
    – MaxW
    Apr 13, 2016 at 20:41
  • $\begingroup$ @MaxW My team has limited room for desk space, and even though my company doesn't sweat the details, I would still like to investigate. $\endgroup$
    – Gram
    Apr 14, 2016 at 0:47
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    $\begingroup$ Is there a way to vote against the "put on hold"? From the title of the question it is clear the OP wants to know is this is "theoretically" feasible, if physics allows or forbids such a device. $\endgroup$
    – L. Levrel
    Apr 15, 2016 at 12:26

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LCD displays use three layers:

  • a polarizer, which polarizes the light produced by the backlight system
  • a liquid crystal, which has the ability to twist or not the direction of polarization of light, controlled by an electric field
  • another polarizer, called analyzer, stops or not the light out of the liquid crystal, depending on it having rotated or not the direction of polarization

The trick you're referring to means removing the analyzer: the light then comes out of the screen whatever the state of the liquid crystal, the screen looks uniformly white (the eye is [almost totally] insensitive to polarization).

If you leave the analyzer in place, the display is fully functional: where light is stopped, the pixel is black and there's nothing you can do about it.

No additional layer can ever "get back" light that has been absorbed, to make the screen all white. Just like hanging windows onto walls will not make daylight enter a room.

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    $\begingroup$ I fail to see how this addresses the actual question asked by OP. $\endgroup$
    – Kyle Kanos
    Apr 13, 2016 at 22:53
  • $\begingroup$ Informative, but I am a bit confused. If I add an "Analyzer" on top, that would stop all light? And if I add a "Polarizer" on the top it would not do anything? $\endgroup$
    – Gram
    Apr 14, 2016 at 0:52
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    $\begingroup$ @Gram: "analyzer" is just a name given to a polarizer fulfilling a specific function. Yes, if you put a polarizer on top of an LCD, in some orientation you stop all light (if you have or can borrow polarized sunglasses it's easy to test: the usual orientation is tilting the glasses 45° clockwise; or anticlockwise sometimes). $\endgroup$
    – L. Levrel
    Apr 14, 2016 at 19:45
  • $\begingroup$ @Kyle: Let me repeat my conclusion: "if you leave the analyzer in place, the display is fully functional (...) and there's nothing you can do about it". $\endgroup$
    – L. Levrel
    Apr 14, 2016 at 19:47
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    $\begingroup$ Gram says "please keep it basic", so I think he would like to get explanations, not a mere "no". (This is a physics site, not a DIY forum.) I edited the answer to try and make it even more clear why adding anything will not help. $\endgroup$
    – L. Levrel
    Apr 14, 2016 at 20:08

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