MSNBC said polarized lenses do not block UV rays

Discussion in 'Optometry Archives' started by Gary, Aug 8, 2005.

  1. Gary

    Gary Guest

    MSNBC said polarized lenses do not block UV rays. They did a survey in which
    inexpensive sunglasses, down to $2, all blocked at least 99% of the UV rays.

    I checked with a few web sites and they sell polarized sunglasses that also
    do UVA and UVB blocking. Should I assume that polarized glass does not block
    these rays but the manufacturers simply ad a coating as a final process?

    Thanks,

    Gary
     
    Gary, Aug 8, 2005
    #1
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  2. Gary

    Gary Guest

    What is UVb?

     
    Gary, Aug 8, 2005
    #2
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  3. Gary

    LarryDoc Guest

    You're attempting, I think, to describe photochromic lenses---a material
    that changes darkness upon exposure to UV energy. But incorrect in any
    event. As is the information presented at MSNBC.

    Polarized lenses can be made of glass or plastic, both materials will
    inherently block UV/b energy and most polarizing lenses block UV/a as
    well. Polarizing lenses consist of two layers of glass or plastic with
    a polarizing plastic layer in between as a laminate or two single layers
    bonded together. Horizontally reflected light is "cancelled" nearly 100%
    and as such there is complete blocking of all light, including UV. Light
    at other angles is reduced by the absorption level of the material,
    usually 75-90% and UV is blocked accordingly or at even high levels
    depending upon the material or applied coatings.

    --LB, O.D.
     
    LarryDoc, Aug 8, 2005
    #3
  4. Gary

    p.clarkii Guest

    these are two different things. polarized lenses might very well not
    block UV light.
     
    p.clarkii, Aug 9, 2005
    #4
  5. Gary

    LarryDoc Guest

    The "ultraviolet" part of the solar light spectrum is divided into three
    wavelength bands, A, B and C. UV-b is the wavelength which can cause
    sunburns, tanning, skin cancer, cataracts and other tissue changes. "UV"
    and the wavelength cut off that calls one A and one B is just a number.
    The damage caused by the rays does not pay attention to the numbers and
    it is clear that the shorter the wavelength (C being the shortest and
    deadly to living things), the more risk of damage to living tissue.

    Think of C as catastrophic, B as bad and A is less bad approaching
    alright and visible.

    LB, O.D.
     
    LarryDoc, Aug 9, 2005
    #5
  6. Gary

    Guest Guest

    There is nothing intrinsic to polarized film of the Polaroid type that would
    make them UV blocking. On the other hand, many materials do block UV and I
    am pretty sure that nothing is purposely done to avoid such materials. Even
    the polarized glasses I have bought at the 99ยข store were claimed UV
    blocking. I'd be a bit more wary of glasses coming from China or any third
    or fourth world country.

    Bill
     
    Guest, Aug 9, 2005
    #6
  7. Gary

    Gary Guest

    That explains so much about UVa and UVb. Is UVc blocked by all glasses. I
    can't recall ever seeing it advertised.
     
    Gary, Aug 9, 2005
    #7
  8. Gary

    LarryDoc Guest

    UV-c is blocked by the earth's atmosphere-----better be careful about
    protecting it or we all become extinct.

    --LB, O.D.
     
    LarryDoc, Aug 9, 2005
    #8
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