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While waiting for a 3D movie to start, I was playing with the glasses they give you. I understand each lens has different polarized filters, so the left and right superimposed images on the screen go to the correct eyes.

The first thing that tripped me up was that rotating the glasses didn't affect the light that passes through it. After searching I bit I discovered about circular polarization, which ignores the angle of the filter and seems to be the standard for cinema glasses.

The second thing that tripped me up were the wall lamps. When looking through one lens, the light seemed to have a bluish color. From the other, a reddish/orange color. It was subtle, but other people confirmed seeing it.

I figured the lamp's white light had blue and red components, which are of different wavelengths (almost opposite in the visible spectrum, if I remember correctly), but what does the wavelength have to do with circularly polarized filters? And if this line of thought is correct, why does it seems to divide the visible spectrum?

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    $\begingroup$ I could imagine the glass around the lamp having a single, chiral, crystalline structure that results in polarization, and that it affects some wavelengths more than others. On the other hand, that is the kind of effect you should have to work hard to get - not something you'd accidentally do when mass producing theater lights. $\endgroup$
    – user10851
    Commented Feb 7, 2013 at 3:20
  • $\begingroup$ I noticed the effect on all lamps along the walls, and I think even the tiny lights on the ground that help you find your seat (those were too small and the effect on them too subtle). Nothing else looked that way, only the light sources, obviously excluding the screen. I didn't think of looking at my phone to compare. $\endgroup$
    – BoppreH
    Commented Feb 7, 2013 at 3:38
  • $\begingroup$ Look at your cellphone screen (preferable make it white by loading a blank page in your browser). You'll see a rainbowy thing. $\endgroup$
    – Manishearth
    Commented Feb 7, 2013 at 7:35
  • $\begingroup$ related: physics.stackexchange.com/questions/9814/… $\endgroup$
    – user10851
    Commented Feb 10, 2013 at 4:46

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Some 3D glasses use narrow-band filters rather than polarization, which is quite clever.

See http://en.wikipedia.org/wiki/Dolby_3D for details.

The reason the light looked different through each eye is that the light spectrum isn't uniform across the visible wavelength. Thus, when different parts of that spectrum are viewed (through the left or right lenses), you get light that's not quite white, and not quite the same.

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  • $\begingroup$ "Dolby 3D glasses are more expensive and fragile [...] and are not considered disposable." This rings a bell, the glasses even had RFID tags to prevent theft. Interesting to know it has nothing to do with polarization. $\endgroup$
    – BoppreH
    Commented Feb 7, 2013 at 15:07

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