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Science Forum Index » Medicine - Vision Forum » polarized sunglasses
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| Bucky |
 Posted: Mon Jan 29, 2007 3:50 am |
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I bought a quality pair of polarized sunglasses (Hobie, $60 sale/$160
retail) for driving purposes, especially to help in daylight rainy
conditions. I read about the theory of polarized light, and thought it
would be a great improvement over regular sunglasses. However, I've a
been quite disappointed in their performance.
Whenever I came across a situation that I thought should make a
difference (like sun reflecting off a wet road, or drizzling
conditions), I compared the polarized sunglasses vs a non-polarized $5
sunglasses. I honestly couldn't notice any difference in glare
reduction.
On the other hand, polarized lenses had some negative effects. LCD
displays (radio, odometer) have a disconcerting shimmer (because my L
and R eyes see different brightness due to their different angles).
When I looking at other cars' windshields, I see a disconcerting
effect of a grid of spots (possibly due to safety glass?) And I can
barely see a rainbow! =)
What are other people's experiences with polarized sunglasses? They'd
probably be really great if you're at the beach or on the water, but
for land and driving use, I think I'll get non-polarized next time.
http://www.hobiepolarized.com/eyewear.aspx |
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| Mark A |
| Posted: Mon Jan 29, 2007 4:12 am |
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"Bucky" <uw_badgers@email.com> wrote in message
news:1170057000.658437.227290@s48g2000cws.googlegroups.com...
Quote: I bought a quality pair of polarized sunglasses (Hobie, $60 sale/$160
retail) for driving purposes, especially to help in daylight rainy
conditions. I read about the theory of polarized light, and thought it
would be a great improvement over regular sunglasses. However, I've a
been quite disappointed in their performance.
Whenever I came across a situation that I thought should make a
difference (like sun reflecting off a wet road, or drizzling
conditions), I compared the polarized sunglasses vs a non-polarized $5
sunglasses. I honestly couldn't notice any difference in glare
reduction.
On the other hand, polarized lenses had some negative effects. LCD
displays (radio, odometer) have a disconcerting shimmer (because my L
and R eyes see different brightness due to their different angles).
When I looking at other cars' windshields, I see a disconcerting
effect of a grid of spots (possibly due to safety glass?) And I can
barely see a rainbow! =)
What are other people's experiences with polarized sunglasses? They'd
probably be really great if you're at the beach or on the water, but
for land and driving use, I think I'll get non-polarized next time.
http://www.hobiepolarized.com/eyewear.aspx
In order to provide optimum polarization, the glare must be coming from a
specific angle. A polarized lens "effectively" has thousands of small slits
that blocks out direct reflections of the sun (sort of like Venetian blinds)
but still let light in. But the slits must be at the correct angle, just
like blinds can be adjusted to block out the direct sun but still let most
of the light in.
A polarized filter used on cameras can be rotated so the slits are aligned
correctly for the glare in a particular scene. In eye wear, the manufacturer
just assumes the glare is coming from a particular angle (since obviously
the eye lens cannot be rotated), and if your glare comes from a different
angle than designed for, it will not be blocked. In other words, a polarized
lens cannot block glare from all angles at the same time. |
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| Bucky |
| Posted: Mon Jan 29, 2007 4:34 am |
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On Jan 29, 12:12 am, "Mark A" <nob...@nowhere.com> wrote:
Quote: if your glare comes from a different
angle than designed for, it will not be blocked. In other words, a polarized
lens cannot block glare from all angles at the same time.
Right. And from my experience, polarized sunglasses don't make any
noticeable improvements in driving conditions, and even have some
negative effect. Maybe they're better for beach/ocean/lake conditions,
but not on land. |
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| Mike Tyner |
| Posted: Mon Jan 29, 2007 12:37 pm |
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"Bucky" <uw_badgers@email.com> wrote
Quote: Right. And from my experience, polarized sunglasses don't make any
noticeable improvements in driving conditions, and even have some
negative effect. Maybe they're better for beach/ocean/lake conditions,
but not on land.
They're a mixed blessing, for sure.
There are a couple of demonstrable improvements for driving, but they don't
appeal to everyone and for some, the peculiarities like windshield spots
outweigh the benefits.
On the plus side, polarized glasses dramatically reduce windshield
reflections when you store a map or route sheet or clipboard on the dash.
Most people won't leave white paper on the dashboard, because this
particular angle creates disabling reflections in full sun, which drop by
about 80% with "correctly" polarized lenses. Of course, it only works
straight-ahead. Polarized lenses actually _increase_ glare over a small area
in front of the passenger. His clipboard will bother you, your clipboard
won't.
The fact you're seeing "spots" in side and rear windshields confirms that
your lenses are effectively polarized. The "spots" are interspersed with
"holes" you can see through, which all turn to bright nothingness when you
take off the glasses.
Occasionally, sunglasses get made with the orientations exactly 90 degrees
_off_. In that case, all drugstore sunglasses look totally black and the
dashboard reflections are intense, rather than subdued.
-MT |
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| Salmon Egg |
| Posted: Mon Jan 29, 2007 8:01 pm |
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On 1/28/07 11:50 PM, in article
1170057000.658437.227290@s48g2000cws.googlegroups.com, "Bucky"
<uw_badgers@email.com> wrote:
Quote: I bought a quality pair of polarized sunglasses (Hobie, $60 sale/$160
retail) for driving purposes, especially to help in daylight rainy
conditions. I read about the theory of polarized light, and thought it
would be a great improvement over regular sunglasses. However, I've a
been quite disappointed in their performance.
High quality expensive polarized glasses do not give you significant
improvement over any non-distorting polarized glasses. I get mine from the
99¢ store when I can.
Quote:
Whenever I came across a situation that I thought should make a
difference (like sun reflecting off a wet road, or drizzling
conditions), I compared the polarized sunglasses vs a non-polarized $5
sunglasses. I honestly couldn't notice any difference in glare
reduction.
These glasses work best when light reflects off a surface at the Brewster
angle. The Brewster angle is related to the index of refraction of the
reflecting/scattering surface. Yes, black asphalt does indeed have a
refractive index. Technically, absorbing surfaces have what is called a
complex refractive index. At the Brewster angle, only light with its
electrical field parallel to the surface gets reflected and that is almost
totally removed by the polarizer. Away from the Brewster angle, some
vertically oriented light will get through.
As the sun rises and falls from dawn to dusk, the angle of reflection
changes. Depending on the time of the year and time of the day, you may
actually get reflection at the Brewster angle.
I found such glasses very useful for fly fishing. At times, it make small
flies highly visible against the glare reflected off of the water. Toward
dawn or dusk, the glare suppression is greatly reduced and getting the extra
light by not using the polarizing glasses often gave better seeing even with
the glare.
Quote:
On the other hand, polarized lenses had some negative effects. LCD
displays (radio, odometer) have a disconcerting shimmer (because my L
and R eyes see different brightness due to their different angles).
When I looking at other cars' windshields, I see a disconcerting
effect of a grid of spots (possibly due to safety glass?) And I can
barely see a rainbow! =)
On my Toyota, the polarization state of the odometer was exactly
incorrectly. It would cost no more to do it correctly for new models.
The spots you see arise from the stress in the windshield. Light gets
partially polarized when scattered in the atmosphere. The blue sky,
scattered by aerosols and air molecules is partially polarized. This
scattered light's polarization state gets modified going through the
stressed glass and adhesive. As a consequence light is absorbed in the
polarizer as a function of windshield stress.
Quote:
What are other people's experiences with polarized sunglasses? They'd
probably be really great if you're at the beach or on the water, but
for land and driving use, I think I'll get non-polarized next time.
Actually, I find polarized glasses useful for driving into glare, but the
cannot be relied upon to give good performance all the time. You may notice
mirages that look like water in the road at dips. Polarized glasses help get
rid of that.
-- Fermez le Bush--about two years to go. |
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| The Real Bev |
| Posted: Tue Jan 30, 2007 8:30 pm |
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Salmon Egg wrote:
Quote: uw_badgers@email.com> wrote:
I bought a quality pair of polarized sunglasses (Hobie, $60 sale/$160
retail) for driving purposes, especially to help in daylight rainy
conditions. I read about the theory of polarized light, and thought it
would be a great improvement over regular sunglasses. However, I've a
been quite disappointed in their performance.
High quality expensive polarized glasses do not give you significant
improvement over any non-distorting polarized glasses. I get mine from the
99¢ store when I can.
Likewise, but I haven't seen any polarized glasses there. Big Five Sporting
Goods, however, has some dandy polarized glasses for $5 or maybe $7 on sale.
If you don't see them, ask if they have any of the $5 "fisherman's"
sunglasses left. I like them better than my fancy Oakley M-Frames (yard
sale for a buck, do you think I'm nuts enough to spend that much on
something I can break or lose, which is exactly what happened?).
I really like the polarized patterns in tempered auto glass.
--
Cheers, Bev
=================================================================
"In all recorded history there has not been one economist who has
had to worry about where the next meal would come from."
-- Peter S. Drucker, who invented management |
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