Streak in Polarized Wraparound Sunglasses

[Caliban]

My new, first time ever, Oakley partial wraparound, prescripton, polarized
sunglasses arrived Monday. I tried them out while bicycling yesterday. At
certain angles, a mostly vertical thin blue streak appears in the right
lens. I can't get it to appear in the left lens.

Is this a characteristic of polarized glasses? Wraparounds? Is there
anything the manufacturer or I can do to eliminate this?

The sunglasses otherwise seem fine, but for what I paid, if I have to live
with the blue streak at certain angles, this may be my first and last pair
of Oakleys.

[Repeating Decimal]

Post by Caliban
My new, first time ever, Oakley partial wraparound, prescripton, polarized
sunglasses arrived Monday. I tried them out while bicycling yesterday. At
certain angles, a mostly vertical thin blue streak appears in the right
lens. I can't get it to appear in the left lens.
Is this a characteristic of polarized glasses? Wraparounds? Is there
anything the manufacturer or I can do to eliminate this?
The sunglasses otherwise seem fine, but for what I paid, if I have to live
with the blue streak at certain angles, this may be my first and last pair
of Oakleys.

I am not sure exactly what you mean.

It is true that stress in a medium can induce birefringence. This sometimes
shows up with automobile windshields interacting with the polarized light
from the scattered blue sky light.

Bill

[Caliban]

Post by Repeating Decimal

Post by Caliban
My new, first time ever, Oakley partial wraparound, prescripton, polarized
sunglasses arrived Monday. I tried them out while bicycling yesterday. At
certain angles, a mostly vertical thin blue streak appears in the right
lens. I can't get it to appear in the left lens.
Is this a characteristic of polarized glasses? Wraparounds? Is there
anything the manufacturer or I can do to eliminate this?
The sunglasses otherwise seem fine, but for what I paid, if I have to live
with the blue streak at certain angles, this may be my first and last pair
of Oakleys.

I am not sure exactly what you mean.
It is true that stress in a medium can induce birefringence. This sometimes
shows up with automobile windshields interacting with the polarized light
from the scattered blue sky light.

As I approximately face the sun wearing the sunglasses, something like a sun ray appears in my line of
vision. It moves as I move my head, and, if I move enough, it goes away. It's like light waves are
cancelling each other out at certain angles so I see a dark spot.

I saw the (independent) dealer and also called Oakley's 800 number. The clerk agreed the "blue streak"
was present but wasn't sure if anything could be done. We also tried to see if the effect was present
in other Oakley wraparounds. We didn't see it in the others.

Both the dealer and Oakley were polite and said it was okay to send them back and see if there was a
defect. Unfortunately, that takes about 4 weeks round trip.

I did a long bike ride today, about half of it facing the sun. It's not unbearable; I just tilt my head
a little downward and the streak is gone. (On the other hand, doing that regularly is annoying.) But
I'm still curious. The streak is distracting.

Thanks for the tip about the possible stress in the material. That's a lead...

[Caliban]

Update:
I went on a four-hour bike ride yesterday, about half of which was facing the
sun so I saw the blue streak for a good deal
of the time. Today I went out on some errands wearing my sunglasses, and, try as
I could, I couldn't get the blue streak back. So I'm pleased. I like the
wraparound a lot -- much better wind protection.

As Repeating Decimal suggested, perhaps there was stress in the lens material,
and it subsequently "relaxed." E.g. perhaps the lenses were coming to
equilibrium with the temperature and humidity where I am? They were shipped from
over 500 miles away. Or the minor adjustment the clerk made to tighten the
frames threw things a bit out of whack?

Any way, all's well. :-)

[Repeating Decimal]

Post by Caliban
I went on a four-hour bike ride yesterday, about half of which was facing the
sun so I saw the blue streak for a good deal
of the time. Today I went out on some errands wearing my sunglasses, and, try as
I could, I couldn't get the blue streak back. So I'm pleased. I like the
wraparound a lot -- much better wind protection.
As Repeating Decimal suggested, perhaps there was stress in the lens material,
and it subsequently "relaxed." E.g. perhaps the lenses were coming to
equilibrium with the temperature and humidity where I am? They were shipped from
over 500 miles away. Or the minor adjustment the clerk made to tighten the
frames threw things a bit out of whack?
Any way, all's well. :-)

On this trip, was there blue sky. If the day is heavily overcast, scattered
light may not be highly polarized.

Bill

[Caliban]

Post by Repeating Decimal

Post by Caliban
I went on a four-hour bike ride yesterday, about half of which was facing the
sun so I saw the blue streak for a good deal
of the time. Today I went out on some errands wearing my sunglasses, and,

try

Post by Repeating Decimal

Post by Caliban
as
I could, I couldn't get the blue streak back. So I'm pleased. I like the
wraparound a lot -- much better wind protection.
As Repeating Decimal suggested, perhaps there was stress in the lens material,
and it subsequently "relaxed." E.g. perhaps the lenses were coming to
equilibrium with the temperature and humidity where I am? They were shipped from
over 500 miles away. Or the minor adjustment the clerk made to tighten the
frames threw things a bit out of whack?
Any way, all's well. :-)

On this trip, was there blue sky.

Yes. Hardly any clouds.

It's very bright in general in the part of the country in which I live. It's
high elevation and desert. Sun cancer mecca.

Post by Repeating Decimal
If the day is heavily overcast, scattered
light may not be highly polarized.

I don't follow your reasoning. On heavily overcast days, you would predict what
would happen with polarized sunglasses?

In any case, on the bike trip and on other days, including today, it has been
almost completely cloudless. That is, maybe 1% of the visible sky had a cloud in
it.

[Repeating Decimal]

Post by Caliban
Yes. Hardly any clouds.
It's very bright in general in the part of the country in which I live. It's
high elevation and desert. Sun cancer mecca.

Post by Repeating Decimal
If the day is heavily overcast, scattered
light may not be highly polarized.

I don't follow your reasoning. On heavily overcast days, you would predict what
would happen with polarized sunglasses?
In any case, on the bike trip and on other days, including today, it has been
almost completely cloudless. That is, maybe 1% of the visible sky had a cloud in
it.

Random multiple scattering will reduce the purity of polarization. By not
seeing such a streak, you have confused your issue in my mind. It might also
have something to do with the direction you are facing wrt the sun.

Bill