Polarized sun glasses

Nate Nagel wrote:

Okay I'm officially confused. I always read about how great
polarized glasses are for riding and driving. And back in my
driving days, I had a set of polarized ray-bans that would stay
in the car.

Now I decided to upgrade my Rudy Project cycling sunglasses. I
bit the bullet, and paid far too much money for a pair of their
polarized lenses. The lenses just arrived, and they have a "not
suitable for driving or road use" warning sticker on them.
Anyone have any idea why?

I wrote to them asking this same question, but while I wait for
their official response, I wanted to see if anyone else had this
problem.

Polarized lenses help over water, fishing etc.

I'm sold on them for driving, haven't tried them riding yet. I
have a set of green-tinted polarized prescription Ray-Bans and I
love them to pieces. The one drawback I've found is that they
produce very strange interference patterns when looking out
through car windows with aftermarket tint film, but none of my
personal vehicles are so equipped so this is a non-issue for me.

Try looking at old VW or other tempered glass windshields. The
stress in such glass causes all angles of polarization and these
interfere with sight with Polaroid glasses. Also, the stress
patterns are strikingly visible with such glasses.

I don't know if tempered glass has ever been acceptable for windshields
here in the US, at least for vehicle years likely to be found still on
the road. My '49 Chevy had laminated glass as well as my '55
Studebaker, and while I actually know of another '49 Chevy nearby with
regular license plates on it no less, that's probably getting close to
the upper limit for age of a vehicle as viable transportation. In fact,
back when those cars were built, laminated glass was required on *all*
windows, and it was only later that tempered glass was allowed for side
and rear windows. AFAIK, laminated ("safety") glass is still required
on windshields.

It wasn't then when VW used temepered glass fir windshileds and other
windows. The reason I mention the windshield is that tempered glass
crazes into corn kernel sized partiocles that I'm sure may riders have
seen scattered along roads. However, if the window doesn't fall out,
it remains as a rough "bathroom window" that does not enable seing
objects throug it. For this reason a clear, untemepered circular area
in front of the dirver was anealed to remain transparent in the event
of a rock crasing the window while driving at speed.

http://en.wikipedia.org/wiki/Tempered_glass
http://www.dropgates.com/y2y/glasslogos.html
http://en.sevenload.com/photos/VbJFKjt-Glas-Securit

These windows have circular stress patterns that can be seen with
polarized light or with Polaroid glasses. The window is not polarized
in any orinetation and its polarization is invisible to the human eye.
Polaroid glasses wouold not be useful for driving an old VW (pre 1960)
--
Jobst Brandt

Nate Nagel wrote:

Okay I'm officially confused. I always read about how great
polarized glasses are for riding and driving. And back in my
driving days, I had a set of polarized ray-bans that would stay
in the car.

Now I decided to upgrade my Rudy Project cycling sunglasses. I
bit the bullet, and paid far too much money for a pair of their
polarized lenses. The lenses just arrived, and they have a "not
suitable for driving or road use" warning sticker on them.
Anyone have any idea why?

I wrote to them asking this same question, but while I wait for
their official response, I wanted to see if anyone else had this
problem.

Polarized lenses help over water, fishing etc.

I'm sold on them for driving, haven't tried them riding yet. I
have a set of green-tinted polarized prescription Ray-Bans and I
love them to pieces. The one drawback I've found is that they
produce very strange interference patterns when looking out
through car windows with aftermarket tint film, but none of my
personal vehicles are so equipped so this is a non-issue for me.

Try looking at old VW or other tempered glass windshields. The
stress in such glass causes all angles of polarization and these
interfere with sight with Polaroid glasses. Also, the stress
patterns are strikingly visible with such glasses.

I don't know if tempered glass has ever been acceptable for
windshields here in the US, at least for vehicle years likely to be
found still on the road. My '49 Chevy had laminated glass as well
as my '55 Studebaker, and while I actually know of another '49 Chevy
nearby with regular license plates on it no less, that's probably
getting close to the upper limit for age of a vehicle as viable
transportation. In fact, back when those cars were built, laminated
glass was required on *all* windows, and it was only later that
tempered glass was allowed for side and rear windows. AFAIK,
laminated ("safety") glass is still required on windshields.

It wasn't at the time when VW used tempered glass for windshields and
other windows. The reason I mention the windshield is that tempered
glass crazes into corn kernel sized particles that I'm sure may riders
have seen scattered along roads. However, if the window doesn't fall
out, it remains as a rough "bathroom window" through which one cannot
identify objects. For this reason a clear, untempered circular area
in front of the diver was annealed to remain transparent in the event
of a pebble crazing the window while driving at speed.

http://en.wikipedia.org/wiki/Tempered_glass
http://www.dropgates.com/y2y/glasslogos.html
http://en.sevenload.com/photos/VbJFKjt-Glas-Securit

These windows have circular stress rings that can be seen with
polarized light or with Polaroid glasses. The window is not polarized
in any orientation and its polarization is invisible to the human eye.
Polaroid glasses would not be useful for driving an old VW (pre 1960)

--
Jobst Brandt

wrote:
Nate Nagel wrote:

Okay I'm officially confused. I always read about how great
polarized glasses are for riding and driving. And back in my
driving days, I had a set of polarized ray-bans that would stay
in the car.

Now I decided to upgrade my Rudy Project cycling sunglasses. I
bit the bullet, and paid far too much money for a pair of their
polarized lenses. The lenses just arrived, and they have a "not
suitable for driving or road use" warning sticker on them.
Anyone have any idea why?

I wrote to them asking this same question, but while I wait for
their official response, I wanted to see if anyone else had this
problem.

Polarized lenses help over water, fishing etc.

I'm sold on them for driving, haven't tried them riding yet. I
have a set of green-tinted polarized prescription Ray-Bans and I
love them to pieces. The one drawback I've found is that they
produce very strange interference patterns when looking out
through car windows with aftermarket tint film, but none of my
personal vehicles are so equipped so this is a non-issue for me.

Try looking at old VW or other tempered glass windshields. The
stress in such glass causes all angles of polarization and these
interfere with sight with Polaroid glasses. Also, the stress
patterns are strikingly visible with such glasses.

I don't know if tempered glass has ever been acceptable for windshields
here in the US, at least for vehicle years likely to be found still on
the road. My '49 Chevy had laminated glass as well as my '55
Studebaker, and while I actually know of another '49 Chevy nearby with
regular license plates on it no less, that's probably getting close to
the upper limit for age of a vehicle as viable transportation. In fact,
back when those cars were built, laminated glass was required on *all*
windows, and it was only later that tempered glass was allowed for side
and rear windows. AFAIK, laminated ("safety") glass is still required
on windshields.

It wasn't then when VW used temepered glass fir windshileds and other
windows. The reason I mention the windshield is that tempered glass
crazes into corn kernel sized partiocles that I'm sure may riders have
seen scattered along roads. However, if the window doesn't fall out,
it remains as a rough "bathroom window" that does not enable seing
objects throug it. For this reason a clear, untemepered circular area
in front of the dirver was anealed to remain transparent in the event
of a rock crasing the window while driving at speed.

http://en.wikipedia.org/wiki/Tempered_glass
http://www.dropgates.com/y2y/glasslogos.html
http://en.sevenload.com/photos/VbJFKjt-Glas-Securit

These windows have circular stress patterns that can be seen with
polarized light or with Polaroid glasses. The window is not polarized
in any orinetation

rubbish! if that were true, you'd not see the effects! human eyes
don't detect polarizing. another polarizer otoh detects it easily.

and polarizing is not shading.


and its polarization is invisible to the human eye.
Polaroid glasses wouold not be useful for driving an old VW (pre 1960)

Under certain conditions and directions, light from the sky is polarized. A
windshield with stresses rotates the direction of polarization, so that,
when viewed through a Polaroid filter (the glasses) the stresses become
visible. This is how a polarimiter is used to display stresses.

Leo Lichtman wrote:
Under certain conditions and directions, light from the sky is polarized.

correct.


A
windshield with stresses rotates the direction of polarization,

a polarizer polarizes. it blocks that which is not correctly oriented.

so that,
when viewed through a Polaroid filter (the glasses) the stresses become
visible.

the interaction is between the polarizing filter and the polarizing
glass, and this happens even with unpolarized light sources.


This is how a polarimiter is used to display stresses.

indeed.

On May 12, 8:39 pm, jim beam wrote:
wrote:

These windows have circular stress patterns that can be seen with
polarized light or with Polaroid glasses. The window is not polarized
in any orinetation

rubbish! if that were true, you'd not see the effects! human eyes
don't detect polarizing. another polarizer otoh detects it easily.

and polarizing is not shading.


Careful there. I have not seen the windshields to which Jobst
refers. However, stress in materials such as glass or plastic
can introduce birefringence (anisotropic index of refraction),
which can then be observed with a polarizer. You may need
the combination of illumination by polarized light (common
since the blue sky is polarized) and viewing through a polarizer.

Here's a good example in plastic:
http://www.oberlin.edu/physics/catal...fringence.html
In the experiment described, two polarizers are used
(since the illumination is provided by an unpolarized
overhead projector) and the birefringent material is
placed between.

A birefringent material is not itself polarized. If this is
the cause of the phenomenon Jobst is describing, he
described it accurately.

Ben

Living in a country with very harsh sunlight and glare (Australia), I
wear polarised sunglasses all the time. I have never encountered the
windshield stress pattern effect when sitting inside a car looking out,
although it is fairly obvious when walking down the street and looking
at windshields on older cars.

The only time I've had problem with visibility and polarised lenses is
in flat light conditions, although I suspect you have more of that in
Europe than we do down here.


--
matagi

wrote:
On May 12, 8:39 pm, jim beam wrote:
wrote:

These windows have circular stress patterns that can be seen with
polarized light or with Polaroid glasses. The window is not polarized
in any orinetation
rubbish! if that were true, you'd not see the effects! human eyes
don't detect polarizing. another polarizer otoh detects it easily.

and polarizing is not shading.


Careful there. I have not seen the windshields to which Jobst
refers.

all modern cars have them for side and rear glass. you can buy cheapo
"fishing" glasses from woolmort for ~$5 if you want to see for yourself.


However, stress in materials such as glass or plastic
can introduce birefringence (anisotropic index of refraction),
which can then be observed with a polarizer. You may need
the combination of illumination by polarized light (common
since the blue sky is polarized) and viewing through a polarizer.

you can use non-polarized light - it's still visible.



Here's a good example in plastic:
http://www.oberlin.edu/physics/catal...fringence.html
In the experiment described, two polarizers are used
(since the illumination is provided by an unpolarized
overhead projector) and the birefringent material is
placed between.

A birefringent material is not itself polarized.

the polarimeter example given by leo. but birefringence arises from
phasing and orientation does it not? unless i misunderstand, that is
itself a polarizing effect for each phase, albeit not dichroic.


If this is
the cause of the phenomenon Jobst is describing, he
described it accurately.

stressed glass is polarizing because of molecular orientation effects.
it may not be as strong as a polymeric dichroic filter, but it's still
present.

Joao de Souza wrote:

I wrote to them asking this same question, but while I wait for their
official response, I wanted to see if anyone else had this problem.

Just got a response from Rudy Project. Apparently that sticker is
required by law in Australia on all polarized glasses. They believe I
somehow received a lens that was supposed go down under by mistake.

But Jobst has a good point about not being able to see wet spots on the
road.........

On 2008-05-13, Leo Lichtman wrote:
Under certain conditions and directions, light from the sky is polarized. A
windshield with stresses rotates the direction of polarization, so that,
when viewed through a Polaroid filter (the glasses) the stresses become
visible. This is how a polarimiter is used to display stresses.

Yes, and you can see the stresses in your windscreen if it's the older
toughened type (but very few cars still have those).

Polarized glasses are especially good for driving/riding IMO because the
glare reflecting from the road and off the backs of cars is itself
polarized the other way from the glasses so they really cut it out.