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RealD Glasses and the polarized effect.

  1. Feb 1, 2010 #1
    Well I recently watched Avatar in 3D.

    Fascinated, I took the glasses home as a memoire of the first 3D movie I have seen.

    I kept the glasses on and then took them off to observe. I understood that in order for you to see things in 3D, you would need at least two projectors, one with a polarizing lens tilted clockwise, another in the opposite direction for the other projector.. etc.

    Out of sheer randomness, I flipped my 3D glasses over, looked through one eye through one side/lens and began tilting it. I did this in front of my LCD screen and noticed that if I tilted it a certain degree(seemed like 45 degrees), my entire screen would become blank to that one eye. Removing the lens from my eye stopped this LCD blackness.
    I understand this occured because of the polarizing lens inside of the monitor.

    Then I glanced at my lamp, then at my old Memorex TV(it has a VCR player built in, just so you know how old it is). I would tilt the lens, but to no avail. I tilted it the other way, again, nothing new happened.
    Then, I noticed something in the corner of my eye. My empty plastic iPod case had some of the light reflected on it, and it so happened to be in my field of vision. I tilted the lenses and to my amazement, the light being reflected on it dimmed. I glanced at the lamp, and tilted the glasses: no dim. I glanced at the TV, and tilted the glasses: no dim.
    I checked the same thing on all surfaces: wall, golden headboard trimmings, polished & shiny wood, sunglasses, even fingernails.

    I then discovered that all reflective surfaces contain a polarizer to some degree.
    Why is this? Why is it that I look at the TV, tilt the glasses, and I don't see any dimmage, but when it's reflected onto another surface I see dimmage?

    Thanks, & it's great to be apart of this forum.
  2. jcsd
  3. Feb 1, 2010 #2


    Staff: Mentor

    Hi Codfish, welcome to PF,

    You are absolutely correct, reflected light is (partially) polarized. This is the effect that makes polarized sunglasses better than non-polarized sunglasses (your 3D glasses are not sunglasses). Next time you are out driving with sunglasses, tilt your head and notice that the glare off the windshields in front of you increases at 45º.
  4. Feb 1, 2010 #3
    There are actually two distinct easily visible sources of polarized light:

    1) Reflection off of dielectric (non-metallic) surfaces. This is due to reflection at Brewsters angle. See

    2) Blue-sky polarization. The visible light from a very clear blue sky at 90 degrees from the Sun is 100% polarized. This is due to Rayleigh scattering. See

    Bob S
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