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?