polarized sunglasses

Discussion in 'Glasses' started by Bucky, Jan 29, 2007.

  1. Bucky

    Bucky Guest

    I bought a quality pair of polarized sunglasses (Hobie, $60 sale/$160
    retail) for driving purposes, especially to help in daylight rainy
    conditions. I read about the theory of polarized light, and thought it
    would be a great improvement over regular sunglasses. However, I've a
    been quite disappointed in their performance.

    Whenever I came across a situation that I thought should make a
    difference (like sun reflecting off a wet road, or drizzling
    conditions), I compared the polarized sunglasses vs a non-polarized $5
    sunglasses. I honestly couldn't notice any difference in glare

    On the other hand, polarized lenses had some negative effects. LCD
    displays (radio, odometer) have a disconcerting shimmer (because my L
    and R eyes see different brightness due to their different angles).
    When I looking at other cars' windshields, I see a disconcerting
    effect of a grid of spots (possibly due to safety glass?) And I can
    barely see a rainbow! =)

    What are other people's experiences with polarized sunglasses? They'd
    probably be really great if you're at the beach or on the water, but
    for land and driving use, I think I'll get non-polarized next time.

    Bucky, Jan 29, 2007
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  2. Bucky

    Mark A Guest

    In order to provide optimum polarization, the glare must be coming from a
    specific angle. A polarized lens "effectively" has thousands of small slits
    that blocks out direct reflections of the sun (sort of like Venetian blinds)
    but still let light in. But the slits must be at the correct angle, just
    like blinds can be adjusted to block out the direct sun but still let most
    of the light in.

    A polarized filter used on cameras can be rotated so the slits are aligned
    correctly for the glare in a particular scene. In eye wear, the manufacturer
    just assumes the glare is coming from a particular angle (since obviously
    the eye lens cannot be rotated), and if your glare comes from a different
    angle than designed for, it will not be blocked. In other words, a polarized
    lens cannot block glare from all angles at the same time.
    Mark A, Jan 29, 2007
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  3. Bucky

    Bucky Guest

    Right. And from my experience, polarized sunglasses don't make any
    noticeable improvements in driving conditions, and even have some
    negative effect. Maybe they're better for beach/ocean/lake conditions,
    but not on land.
    Bucky, Jan 29, 2007
  4. Bucky

    Mark A Guest

    Yes, I suspect the Hobie sunglasses are designed glare coming off the water,
    not straight in front of you. Hobie started out as a watersports company
    making surfboards and small sailboats.
    Mark A, Jan 29, 2007
  5. Bucky

    Salmon Egg Guest

    High quality expensive polarized glasses do not give you significant
    improvement over any non-distorting polarized glasses. I get mine from the
    99¢ store when I can.
    These glasses work best when light reflects off a surface at the Brewster
    angle. The Brewster angle is related to the index of refraction of the
    reflecting/scattering surface. Yes, black asphalt does indeed have a
    refractive index. Technically, absorbing surfaces have what is called a
    complex refractive index. At the Brewster angle, only light with its
    electrical field parallel to the surface gets reflected and that is almost
    totally removed by the polarizer. Away from the Brewster angle, some
    vertically oriented light will get through.

    As the sun rises and falls from dawn to dusk, the angle of reflection
    changes. Depending on the time of the year and time of the day, you may
    actually get reflection at the Brewster angle.

    I found such glasses very useful for fly fishing. At times, it make small
    flies highly visible against the glare reflected off of the water. Toward
    dawn or dusk, the glare suppression is greatly reduced and getting the extra
    light by not using the polarizing glasses often gave better seeing even with
    the glare.
    On my Toyota, the polarization state of the odometer was exactly
    incorrectly. It would cost no more to do it correctly for new models.

    The spots you see arise from the stress in the windshield. Light gets
    partially polarized when scattered in the atmosphere. The blue sky,
    scattered by aerosols and air molecules is partially polarized. This
    scattered light's polarization state gets modified going through the
    stressed glass and adhesive. As a consequence light is absorbed in the
    polarizer as a function of windshield stress.
    Actually, I find polarized glasses useful for driving into glare, but the
    cannot be relied upon to give good performance all the time. You may notice
    mirages that look like water in the road at dips. Polarized glasses help get
    rid of that. Bill
    -- Fermez le Bush--about two years to go.
    Salmon Egg, Jan 30, 2007
  6. Bucky

    The Real Bev Guest

    Likewise, but I haven't seen any polarized glasses there. Big Five Sporting
    Goods, however, has some dandy polarized glasses for $5 or maybe $7 on sale.
    If you don't see them, ask if they have any of the $5 "fisherman's"
    sunglasses left. I like them better than my fancy Oakley M-Frames (yard
    sale for a buck, do you think I'm nuts enough to spend that much on
    something I can break or lose, which is exactly what happened?).

    I really like the polarized patterns in tempered auto glass.

    Cheers, Bev
    "In all recorded history there has not been one economist who has
    had to worry about where the next meal would come from."
    -- Peter S. Drucker, who invented management
    The Real Bev, Jan 31, 2007
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