Sunglasses on are polarized on the wrong axis

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VicTek - 17 Sep 2006 15:35 GMT

I understand that polarization reduces glare by filtering out light on one
axis. Well, I purchased a pair of polarized "clip-ons" and they seem to be
filtering on the wrong axis. Specifically, when I put them on they do not
reduce glare at all, but if I just hold the lens in front of one eye and
rotate it 90 degrees the glare is gone. Is there consensus regarding what
axis polarized lenses are supposed to filter? Are my sunglass clip-ons
"defective" because they are filtering incorrectly or is the axis arbitrary
and in my case the clip-ons are simply useless? <g> I can return them, but
I'd like to find a pair that work.

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Mike Tyner - 17 Sep 2006 17:02 GMT

>I understand that polarization reduces glare by filtering out light on one
>axis. Well, I purchased a pair of polarized "clip-ons" and they seem to be
>filtering on the wrong axis. Specifically, when I put them on they do not
>reduce glare at all, but if I just hold the lens in front of one eye and
>rotate it 90 degrees the glare is gone. Is there consensus regarding what
>axis polarized lenses are supposed to filter?

Absolutely.

The physics forces us to choose the orientation of reflections we eliminate,
either from horizontal or vertical surfaces (or something in between).

The most commonly-encountered reflections are horizontal, like water and
windshields. So properly-made polarized lenses will dramatically reduce
reflections from these surfaces, but the effect on windshields only works
well in the straight-ahead position.

Vertical surface reflections are relatively rare. But polarized lenses will
appear to _enhance_ reflections from vertical surfaces, like when you stand
in front of a store window and look obliquely to the sides.

> Are my sunglass clip-ons "defective" because they are filtering
> incorrectly or is the axis arbitrary and in my case the clip-ons are
> simply useless? <g>

In my experience, the polarizing quality of stamped-out, cheap clipons often
exceeds that of custom-edged lenses.

To test them, put on _another_ pair of polarized lenses and hold up the
clipons to a diffuse light source, then rotate them about the line-of-sight.
Then turn them around and look from the other direction.

-MT, OD

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Quick - 18 Sep 2006 00:09 GMT

> The most commonly-encountered reflections are horizontal,
> like water and windshields. So properly-made polarized
> lenses will dramatically reduce reflections from these
> surfaces, but the effect on windshields only works well
> in the straight-ahead position.

True. These are the more "dazzling" kind. In addition to these
I think polarization is even more beneficial blocking the glare
off of concrete, sand, and that sort of thing that causes fatigue
and eye strain over time. Most people live in the city and/or spend
a lot of time in a car. So one is the immediately blinding type of
glare and another the glare that causes fatigue and strain over
some time.

-Quick (big fan of polarization)

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Salmon Egg - 18 Sep 2006 05:50 GMT

On 9/17/06 9:02 AM, in article
1OGdnWETUq5d7JDYnZ2dnUVZ_sWdnZ2d@giganews.com, "Mike Tyner"
<mtyner@mindspring.com> wrote:

>> I understand that polarization reduces glare by filtering out light on one
>> axis. Well, I purchased a pair of polarized "clip-ons" and they seem to be
[quoted text clipped - 29 lines]
>
> -MT, OD

There is no doubt that clip-on Polaroids work. I have used cheap (99¢ store)
versions for many years while fishing to block glare off of the water. It is
certainly possible that the "lenses" were not cut properly from the sheet
polarizer. I have a liquid crystal odometer in my Toyota van that has
incorrect polarizer orientation. I cannot see the display while wearing the
clip-ons.

To check out your clip-ons, borrow a pair that you know works from a happy
user. Match that up with your pair. If yours is incorrectly oriented, the
combination will block light.

Another test that I use is to look at the reflection of a ceiling light on
the slick floor of a store. If you look through your glasses at the
reflection using approximately an angle of 60 degrees with respect to the
vertical, the image of the light should become virtually invisible.

Bill

-- Fermez le Bush

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VicTek - 19 Sep 2006 04:30 GMT

> On 9/17/06 9:02 AM, in article
> 1OGdnWETUq5d7JDYnZ2dnUVZ_sWdnZ2d@giganews.com, "Mike Tyner"
[quoted text clipped - 63 lines]
>
> Bill

Thanks to all for the helpful replies...

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Jan - 17 Sep 2006 23:17 GMT

VicTek schreef:

> I understand that polarization reduces glare by filtering out light on one
> axis. Well, I purchased a pair of polarized "clip-ons" and they seem to be
[quoted text clipped - 5 lines]
> and in my case the clip-ons are simply useless? <g> I can return them, but
> I'd like to find a pair that work.

Your clip-ons are meant to filter the reflections from horizontal
non-metal surfaces when you are wearing them.

Jan (normally Dutch spoken)

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