From: r_delaney2001@yahoo.com   
      
   On April 7, Phil Hobbs wrote:   
   >> How does polarization of light improve a sunglasses   
   >> quality? Or the "sunglass experience", so to speak -   
   >> That is, I presume the usual definition - the lens   
   >> passes light polarized along a single direction.   
      
   > When light reflects obliquely off a dielectric surface, such as water or   
   > the shiny hood of your car, the reflection is partially polarized,   
   > usually with the vertical polarization much weaker than horizontal.   
   > That means that the electric (E) field is vibrating mostly in the   
   > horizontal direction. (I'm assuming that the surface is horizontal and   
   > the light is coming from above, which is the usual situation outdoors.)   
   > So the glints are polarized and the rest of the scene mostly isn't. (*)   
   > Thus polarizing filters that absorb the horizontal polarization   
   > selectively reduce the glints.   
      
   So this type of filter removes the bit we commonly call glare.   
      
   But there's no free lunch.  So what's the loss or cost?   
      
   > The reason is interesting. The electric field of a light ray   
   > oscillates, but is directed perpendicular to the propagation direction.   
   > At an interface between two non-absorbing dielectrics, the reflected and   
   > refracted beams go in different directions, but their fields have to add   
   > up to the same as the incident wave.  The addition is vectorial, so   
   > there's a difference between horizontal polarization, which stays   
   horizontal, and   
   > vertical, which has to change directions on account of the change in   
   > propagation direction.   
   >   
   > It turns out that when the reflected and refracted rays are at 90   
   > degrees to each other, in vertical polarization the reflection goes to   
   > zero and in horizontal polarization it doesn't. The incidence angle   
   > where this happens is called "Brewster's angle" after its discoverer.   
      
      
   I'm familiar with Brewster angle, but unclear how it affects   
   sunglass performance, i.e. the subjective experience.   
      
   --   
   Rich   
      
   --- SoupGate-Win32 v1.05   
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