Polarized sun glasses

| 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 use the Oakley VR28 lenses, fairly yellow, and find them the best
all-around sunglasses I've used. There are times in extremely-bright
sunlight where something darker might be better, but what I like about the
VR28 is that I can quickly go from light to dark areas on a descent and
still see everything I need to (potholes, water, whatever). Anything darker
and my eyes don't react fast enough to see things in the shaded areas.

--Mike-- Chain Reaction Bicycles
www.ChainReactionBicycles.com


"Brian Huntley" wrote in message
...
| 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:
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.

well, if you're talking the classic example of birefringence, calcite,
both sides of the "split" are polarized.




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."

of course - but all polarization is invisible to the human eye unless
aided in some way.


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.

you would see a little if the light source was polarized. in fact you
/can/ see it - i've been looking for it, and indeed, you can see it in
pretty much any car side or rear glass naked eye if the light it right
[polarized sufficiently - we've had several days like that recently here
in norcal].


Unless, that is, you were already wearing
Polaroid sunglasses.

those kind of polarized lenses are made from strained polymer where
molecular alignment only passes light oriented per the strain direction.
the same effect happens with strained glass, though to a much lesser
degree because glass molecules are so much smaller. you would expect
prismatic coloration from strained glass density differences too.

i think we're arguing around the same subject of principles - the
question is whether the glass is birefringent or polarizing.

examples of [special] strained glass polarizing in application:
http://www.freepatentsonline.com/5430573.html
http://www.patentstorm.us/patents/55...scription.html

Mike Jacoubowsky wrote:
| 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 use the Oakley VR28 lenses, fairly yellow, and find them the best
all-around sunglasses I've used. There are times in extremely-bright
sunlight where something darker might be better, but what I like about the
VR28 is that I can quickly go from light to dark areas on a descent and
still see everything I need to (potholes, water, whatever). Anything darker
and my eyes don't react fast enough to see things in the shaded areas.

that's what jobst is confused about, not polarization. if for some
bizarre reason someone considered polarized lenses somehow were
interfering with their vision, all they have to do is tilt their head a
little to change the polarization angle.




--Mike-- Chain Reaction Bicycles
www.ChainReactionBicycles.com


"Brian Huntley" wrote in message
...
| 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.

"jim beam" wrote in message
...
| Mike Jacoubowsky wrote:
| | 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 use the Oakley VR28 lenses, fairly yellow, and find them the best
| all-around sunglasses I've used. There are times in extremely-bright
| sunlight where something darker might be better, but what I like about
the
| VR28 is that I can quickly go from light to dark areas on a descent and
| still see everything I need to (potholes, water, whatever). Anything
darker
| and my eyes don't react fast enough to see things in the shaded areas.
|
| that's what jobst is confused about, not polarization. if for some
| bizarre reason someone considered polarized lenses somehow were
| interfering with their vision, all they have to do is tilt their head a
| little to change the polarization angle.

I don't think so. Some years ago I had a pretty nasty fall descending the
west side of Alpine Road heading towards Skyline (Jobst will know this
stretch of road quite well). I was wearing polarized glasses, it was fairly
late in the day, and rounding a corner everything went from very bright to
very dark, or at least the road did, and I never saw the change in the road
surface that put me down... hard and fast. It was definitely an effect of
the sunglasses, which I never wore again, and have never ever experienced
anything similar since.

I'm told that newer Oakley polarized lenses are quite different from what
used to be the norm; apparently it's a very light polarization with some
tinting. Not so polarized that you get the extreme effect that causes
trouble, but this is way outside my area of expertise, so for all I know
being a little bit polarized would be like being a little big pregnant.

--Mike-- Chain Reaction Bicycles
www.ChainReactionBicycles.com

In article ,
Joao de Souza 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?


It's an EU thing, if the sunglasses block more than X percent of
visible light, then they need this warning.

_ Booker C. Bense

Booker Bense wrote:
In article ,
Joao de Souza 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?


It's an EU thing, if the sunglasses block more than X percent of
visible light, then they need this warning.

_ Booker C. Bense


makes more sense than freaking about so-called "problems" with
polarization!!!

In article ,
Booker Bense wrote:
In article ,
Joao de Souza 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?


It's an EU thing, if the sunglasses block more than X percent of
visible light, then they need this warning.


I can't find a good online reference, but CE specifies four
classes of sunglass "protection" and all CE Class four ( and
maybe 3 ) have to have the warning about "not suitable for
driving".

_ Booker C. Bense