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I wanted to buy some pieces of linear polarizing films for experiments with polarized LED lights. I could not find any options in local shops nor in Europe Amazon, but some quick search told me that LCD polarizers are usually linear, vertical, horizontal, 45 or 135 degrees. I definitely knew that I don't need circular polarizers but from most materials I found online, it seems that all LCD panels should have linear polarizers because that is crucial part of LCD inner workings. So I found and ordered some Samsung Note and Galaxy LCD polarizers from AliExpress sellers with high reputation and positive reviews.

When I received the polarizers, I was surprised. They do not work as polarizers at all! They pass the light through, no matter how I cross them and even when I look through them at my LCD monitor or at a smartphone screen. When I look at daylight through one of those polarizers, they seem to be just like tinted film. But when two of them are combined or when looking through them at any LCD screen, a strong rainbowing effect appears. So, definitely they are not just a tinted film; they do interact with light in some way.

In comparison, my linearly polarized sunglasses work as expected, blocking almost all the light when I look through them at my LCD monitor (Viewsonic VP2365WB) and my Sansa Clip MP3 player and the light starts coming through if I rotate my head. But the sunglasses do not work as polarizers with my smartphone (HTC One M8S) - I can see the screen no matter how I rotate my head. Thus I deduced that my smartphone does not have linear polarizer, and also that the polarizers I bought are not linear.

So, they might be circular polarizers but I'm not sure because searching for circular polarizers on the Internet gives me results about photography circular polarizers which seem to work somewhat differently to the ones I have.

How can LCD pixels on my smartphone show up if the LC panel is not put behind a linear polarizer? How else does it work and why the polarizers are needed at all?

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closed as off-topic by placeholder, Dave Tweed Jun 30 '16 at 2:07

  • This question does not appear to be about electronics design within the scope defined in the help center.
If this question can be reworded to fit the rules in the help center, please edit the question.

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    \$\begingroup\$ Those don't look like polarizers at all - they look like neutral-density filters. Try buying from a reputable optics company: edmundoptics.com/optics/polarizers/linear-polarizers \$\endgroup\$ – Mark Jun 29 '16 at 22:12
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    \$\begingroup\$ I'm voting to close this question as off-topic because ... POLARIZER PURCHASING \$\endgroup\$ – placeholder Jun 30 '16 at 0:01
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    \$\begingroup\$ @Dave Tweed Because it is related to LCD technology and I intend to use polarizers in combination with LED. \$\endgroup\$ – JustAMartin Jun 30 '16 at 6:59
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    \$\begingroup\$ @placeholder My question is not that much about purchasing but more about the technology - why smartphone screen polarizers in general do not work as I expected (not only the "wrong" ones I bought but also the one on my HTC One M8S screen which shows no light changes when I look at the screen from any angle through my polarized sunglasses? \$\endgroup\$ – JustAMartin Jun 30 '16 at 7:02
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    \$\begingroup\$ @DaveTweed: The OP's point is good. This is related to EE as LCDs are one of the most common applications. I answered and learned from creating my answer as I had to research circular polarisation. \$\endgroup\$ – Transistor Jun 30 '16 at 7:14
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It seems to me that you have been shipped tinted film.

To test for linear polarized film rotate one piece in front of the other. When lined up as laid out in the original sheet they should pass light. When rotated at 90° they should block all light and appear black. (You obviously know this.)

To test for circular polarization:

The simplest test for whether a polarizing filter is really and truly a circular polarizer is very easy. Look through it into a mirror. [In one orientation] light is reflected off the mirror and passes back through. There is some darkening (about 1-2 [camera f-]stops with each pass through the filter). There is very little color cast visible.

Now reverse the filter. Now the mirror image of the filter is very dark.

If you try the same test with a good linear polarizer, there is absolutely no difference on reversing it - the image looks identical, and with minimal color cast.

Source: Beware cheap "circular" polarizers. Text in [ ] are my insertions for clarity as the article is about camera filters.

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  • \$\begingroup\$ But then why also the polarizer on my HTC One M8S screen shows no light changes when I look at the screen from any angle through my polarized sunglasses? Doesn't this mean that smartphone LCD screens use some different mechanism of polarization? \$\endgroup\$ – JustAMartin Jun 30 '16 at 7:07
  • \$\begingroup\$ Also, the ones I bought seem to be more than just a tinted film - they seem to be a tinted film when I look through them at normal daylight, but when I combine two of them or when I look through them at any LCD screen, there appears some kind of really strong rainbow color effect. \$\endgroup\$ – JustAMartin Jun 30 '16 at 7:09
  • \$\begingroup\$ I just tried the mirror test - from that aspect the "wrong" polarizers do not show expected behaviour, they just block the same amount of light, no matter from which side or at which angle I look. The only thing that changes depending from the relative angle between two polarizers, is the rainbow effect - it gets much stronger if I put polarizers at 90°. So, definitely not just tinted film. But also not exactly the circular polarizers as used in photography. \$\endgroup\$ – JustAMartin Jun 30 '16 at 7:26

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