Polarized sun glasses

On 2008-05-13, Joao wrote:
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.........

If it's wet and dry conditions like he described, just assume wet if in
doubt, and you should get to the bottom in one piece.

Joao wrote:

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.

As an Australian buyer and user of polarized sunglasses, that's
news to me. Other than this thread, I've never read any
warning about their use.

Like many others, I much prefer polarized sunglasses when riding
and driving because their glare reduction is maximised exactly
where it's most needed.

I do understand Jobst's concerns, having noted the effect many
times over many decades. If you're riding aggressively enough
for it to matter and there's any question about wet or dry,
either assume the worst or you can rotate your head from the
vertical a little to the left and right. That rotation will
expose a polorized reflection which the glasses had hidden.
Such a reflection /might/ be from water, or it might not.

John

On May 13, 2:41*pm, John Henderson wrote:
Joao wrote:
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.

As an Australian buyer and user of polarized sunglasses, that's
news to me. *Other than this thread, I've never read any
warning about their use.

Like many others, I much prefer polarized sunglasses when riding
and driving because their glare reduction is maximised exactly
where it's most needed.

I do understand Jobst's concerns, having noted the effect many
times over many decades. *If you're riding aggressively enough
for it to matter and there's any question about wet or dry,
either assume the worst or you can rotate your head from the
vertical a little to the left and right. *That rotation will
expose a polorized reflection which the glasses had hidden.
Such a reflection /might/ be from water, or it might not.

I don't wear sunglasses since I have prescription lenses and rarely
ride in blinding bright light in the Pacific Northwest. I do ride in
a lot of rain and the most dangerous condition for me is descending a
twisting road under the trees in dappled light after a rainstorm. The
glare-shadow effect makes it hard for me to detect road hazards in the
shade (typically in corners). I would think that glare reduction would
be helpful in this situation since it might reduce the flash-and-
accommodate syndrome. -- Jay Beattie.

On May 14, 9:41*am, John Henderson wrote:

I do understand Jobst's concerns, having noted the effect many
times over many decades. *If you're riding aggressively enough
for it to matter and there's any question about wet or dry,
either assume the worst or you can rotate your head from the
vertical a little to the left and right. *That rotation will
expose a polorized reflection which the glasses had hidden.
Such a reflection /might/ be from water, or it might not.

Agreed here (in NZ) I wear polarised when driving a car, especially in
morning or late afternoon when the low sun is a hazard. However, even
when I'm walking on a wet pavement I find the odd appearance of the
ground distracting, more-so on the bike. Rather than wondering if I am
looking at a slick patch, or being distracted by the odd appearance of
the road surface, I wear non polarising dark sunnies (I like the
yellow dark type but that;s a personal thing I guess).

Ben C? 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...

If it's wet and dry conditions like he described, just assume wet if
in doubt, and you should get to the bottom in one piece.

Or, take off the Polaroid glasses so you can see which sections of the
road are still wet in a forested descent, as I mentioned.
Conjecturing about it isn't good advice or an answer for why someone
would put a warning sticker:

"The lenses just arrived, and they have a "not suitable for driving or
road use." I explained reasons for the warning sticker. I get the
impression that the counter arguments presented are not from
experience with Polaroid glasses. It reminds me of writers advising
to use low gears when riding on frozen lakes an obvious clue that the
writer never tried it.

It also reminds me of Marco Polo who, historians believe, made up much
of his tales of China, because nowhere does he mention The Great Wall,
glaring proof that he was never there, creating his tales from
seamen's diaries (Incomplete library research).

Jobst Brandt

On May 13, 7:36 pm, Don Mackie wrote:
On May 14, 9:41 am, John Henderson wrote:

I do understand Jobst's concerns, having noted the effect many
times over many decades. If you're riding aggressively enough
for it to matter and there's any question about wet or dry,
either assume the worst or you can rotate your head from the
vertical a little to the left and right. That rotation will
expose a polorized reflection which the glasses had hidden.
Such a reflection /might/ be from water, or it might not.

Agreed here (in NZ) I wear polarised when driving a car, especially in
morning or late afternoon when the low sun is a hazard. However, even
when I'm walking on a wet pavement I find the odd appearance of the
ground distracting, more-so on the bike. Rather than wondering if I am
looking at a slick patch, or being distracted by the odd appearance of
the road surface, I wear non polarising dark sunnies (I like the
yellow dark type but that;s a personal thing I guess).

I used to ride in yellow lenses all winter long, but the change they
made to the sky was what made me move away from them.They're
depressing, at least at these latitudes.

I've been testing a graduated tint set of lenses lately. I think I'll
pass and go back to Foster Grants for sunny days and safety lenses
(clear) for rain and night time.

wrote:
Ben C? 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...

If it's wet and dry conditions like he described, just assume wet if
in doubt, and you should get to the bottom in one piece.

Or, take off the Polaroid glasses so you can see which sections of the
road are still wet in a forested descent, as I mentioned.

or tilt your head a few degrees if you really don't have the ability to
learn to see without expecting glare.



Conjecturing about it isn't good advice or an answer for why someone
would put a warning sticker:

wow, as the king of conjecture yourself, what kind of warning sticker
would you have on your forehead?



"The lenses just arrived, and they have a "not suitable for driving or
road use." I explained reasons for the warning sticker. I get the
impression that the counter arguments presented are not from
experience with Polaroid glasses. It reminds me of writers advising
to use low gears when riding on frozen lakes an obvious clue that the
writer never tried it.

It also reminds me of Marco Polo who, historians believe, made up much
of his tales of China, because nowhere does he mention The Great Wall,
glaring proof that he was never there, creating his tales from
seamen's diaries (Incomplete library research).


cute. but utterly irrelevant in a way only jobst brandt could conceive!

I wear polarized glasses for driving beacuse they reduce effect of
pitted windhield glare, which I suppose is little more thatn LOTS of
tiny glare points off of little faceted chips in the glass. I find
polarized lenses also reduce the distracting effects of reflections of
the car interior on the widshield.

Without having a reflective windhshield on my bikes, I question the
bennefit of polarized lenses for bicycling

After reading all above, I will not wear polarized lenses any longer
when driving my CAR on roads that may be wet, but will continue to
wear in car on dry days.

Regards,

Pat Smith


"The lenses just arrived, and they have a "not suitable for driving or
road use." *I explained reasons for the warning sticker. *I get the
impression that the counter arguments presented are not from
experience with Polaroid glasses. *It reminds me of writers advising
to use low gears when riding on frozen lakes an obvious clue that the
writer never tried it.

Another reason not to use polarized sunglasses while driving/biking is
that they reduce your ability to see depth-of-field. As a mountaineer
I don't use them just for this reason as it makes it difficult to see
how close/far one is to crevasses and other critical navigational
features. For this same reason you don't see to many aviators
(especially those who land on snow or water) using them. Polarized
lenses tend to flatten your visual perception.

On May 12, 10:20 pm, jim beam wrote:
wrote:

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...ptics/birefrin...
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.

That is not how I would describe birefringence. Common
polarizing material as in sunglasses absorbs light of one
polarization, allowing the perpendicular polarization
to pass. (More complex polarizers can be made to beam-split
the two polarizations). A birefringent material has a different
index of refraction for the two polarizations, so both polarizations
are transmitted, but they are refracted differently, which is why
you can see rainbow-like colors if you look through them
with a polarizer.

A birefringent material is not itself a polarizer although
you can use two birefringent crystals to make a beam-splitting
polarizer, as in a Wollaston prism. But now we are
talking about optics, not windshields.

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.

Not in a useful sense. Light passes though the glass and comes
out with a correlation between polarization, incident angle, and
color,
but as Jobst said "its polarization is invisible to the human eye."
It's well known that if you use a polarizing filter or Polaroid
sunglasses to look at the blue sky or reflections off water,
it absorbs some of the light; but if you looked through a piece
of stressed glass at the blue sky or water, you wouldn't see
an effect. Unless, that is, you were already wearing
Polaroid sunglasses.

Ben