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Re: [ATM] blank internal stress checking with polarizers.
Waldo,
> many windshields are polarized these days ;)
>to find out if yours is, get some polarized sunglasses and turn them at an
>angle
>until the image goes dark...
Interesting. If I understood you correctly you are speaking of transmitted
light.
So I took my Polaroid's and went out into the car,
only to find that my windshield is not "polarized".
>FWIW: be careful with cheap polarized sunglasses... i bought some one time
>and
>they weren't aligned with my windshield... i had to take them back because
>i
>couldn't see to drive! ;)
I admit that I never heard about such possibility. If you could not see to
drive
than windshield should be very efficiently "polarizing" the light coming
through it.
In such car you will not need polarizing sunglasses.
If windshields are really polarizing efficiently than direction of
polarization must be standardized so that manufacturers of expensive
Polaroid sunglasses can make them with proper direction. I never heard of
this neither from car sellers nor glasses manufacturers.
>> Wouldn't any piece of glass do the same, like ordinary windows, shop
>> windows even side windows of the car, if light is reflected at required
>> angle?
>not that i'm aware of ;)
While examining windshield of my car I took also a look around. Reflection
from every
glass in vicinity, windows of nearby houses, side windows of nearby cars,
all show that
reflected light was polarized and they darkened accordingly as I rotated my
sunglasses.
Light is partially polarized at every reflection from any object.
Richard Snashal wrote:
>Didn't I hear somewhere that it works even better if you stack a few up?
That is correct. At every partial reflection transmitted light is partially
polarized
at another reflection additional part of transmitted light is polarized and
so on.
The light passing through the stack becomes progressively more and more
polarized
if light enters the stack at or near Brewster angle.
Polarization by reflection is explained for example in :
http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/polref.html
especially about the best angle for polarization (Brewster angle).
Regards
Vladimir.
PS
Goggling for polarized windshields told me that idea is old but never
implemented
by car industry. Perhaps this has changed in the meantime.
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