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Polarized Filters

  1. Aug 22, 2003 #1
    I was playing around with two polarized filters the other day. I was actually on the highway at the time. Something that I noticed when I had them aligned to block out all light, the only light that seemd to make it through was red. It was pretty cool looking to look at all the oncoming car's headlights (which we should know are white) and only seeing little red dots.

    I would imagine this is a result of where red stands on the spectrum. This was actually surprising to me, because I was unaware that the frequancy of light had any impact on polarized filters. Plus even if it does, I would have thought the higher frequencies would be the ones able to penetrate.

    So anyway, question is why red?
  2. jcsd
  3. Aug 22, 2003 #2
    With the two polarizers I have - I can only see blue through them.
  4. Aug 22, 2003 #3


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    Staff: Mentor

    Two good linearly polarized discs will let through precisely ZERO light when oriented at right angles to each other.
  5. Aug 22, 2003 #4


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    Your polarised filters are dodgy?

    Russ: Unless if there is another polarised disc in between out of alignment with the two.
  6. Aug 23, 2003 #5


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    Staff Emeritus
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    A polarizer's effect on light is certainly frequency-dependent. After all, it's just a material made with a lot of closely-spaced lines. The spacing determines the interaction with light. The smaller the spacing, the higher the frequency of light that will interact with it.

    There's no way that two perpindicular polarizers can admit ZERO light -- are you telling me that I can't transmit radio waves or blast some gamma rays through two sets of Ray-Bans? The polarization characteristics of realistic polarizing material is frequency-dependent.

    - Warren
  7. Aug 25, 2003 #6
    And also, couldn't you just add an extra polarized filter such that the outside filters are oriented the same, perpendicular to the middle filter and then allowing the light to once again pass through?
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