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13-05.-2008, 02:46 PM
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#16 |
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Guest
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Re: Polarized sun glasses
On May 12, 8:39 pm, jim beam <spamvor...@bad.example.net> wrote:
> jobst.bra...@stanfordalumni.org wrote: > > These windows have circular stress patterns that can be seen with > > polarized light or with Polaroid glasses. The window is not polarized > > in any orinetation > > rubbish! if that were true, you'd not see the effects! human eyes > don't detect polarizing. another polarizer otoh detects it easily. > > and polarizing is not shading. > Careful there. I have not seen the windshields to which Jobst refers. 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. Here's a good example in plastic: http://www.oberlin.edu/physics/cata...efringence.html 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. If this is the cause of the phenomenon Jobst is describing, he described it accurately. Ben |
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13-05.-2008, 02:50 PM
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#17 |
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Registered User
Join Date: Mar 2006
Location: In a parallel universe
Posts: 3,997
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Re: Polarized sun glasses
Living in a country with very harsh sunlight and glare (Australia), I wear polarised sunglasses all the time. I have never encountered the windshield stress pattern effect when sitting inside a car looking out, although it is fairly obvious when walking down the street and looking at windshields on older cars.
The only time I've had problem with visibility and polarised lenses is in flat light conditions, although I suspect you have more of that in Europe than we do down here. |
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13-05.-2008, 03:20 PM
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#18 |
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Guest
Posts: n/a
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Re: Polarized sun glasses
bjw@mambo.ucolick.org wrote:
> On May 12, 8:39 pm, jim beam <spamvor...@bad.example.net> wrote: >> jobst.bra...@stanfordalumni.org wrote: > >>> These windows have circular stress patterns that can be seen with >>> polarized light or with Polaroid glasses. The window is not polarized >>> in any orinetation >> rubbish! if that were true, you'd not see the effects! human eyes >> don't detect polarizing. another polarizer otoh detects it easily. >> >> and polarizing is not shading. >> > > Careful there. I have not seen the windshields to which Jobst > refers. all modern cars have them for side and rear glass. you can buy cheapo "fishing" glasses from woolmort for ~$5 if you want to see for yourself. > 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/cata...efringence.html > 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. > 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. |
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14-05.-2008, 04:07 AM
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#19 |
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Guest
Posts: n/a
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Re: Polarized sun glasses
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.........  |
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14-05.-2008, 07:12 AM
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#20 |
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Guest
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Re: Polarized sun glasses
On 2008-05-13, Leo Lichtman <l.lichtman@worldnet.att.net> wrote:
> Under certain conditions and directions, light from the sky is polarized. A > windshield with stresses rotates the direction of polarization, so that, > when viewed through a Polaroid filter (the glasses) the stresses become > visible. This is how a polarimiter is used to display stresses. Yes, and you can see the stresses in your windscreen if it's the older toughened type (but very few cars still have those). Polarized glasses are especially good for driving/riding IMO because the glare reflecting from the road and off the backs of cars is itself polarized the other way from the glasses so they really cut it out. |
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14-05.-2008, 07:17 AM
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#21 |
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Guest
Posts: n/a
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Re: Polarized sun glasses
On 2008-05-13, Joao <no@way.jose> 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. |
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14-05.-2008, 07:41 AM
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#22 |
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Guest
Posts: n/a
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Re: Polarized sun glasses
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 |
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14-05.-2008, 09:11 AM
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#23 |
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Guest
Posts: n/a
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Re: Polarized sun glasses
On May 13, 2:41*pm, John Henderson <jhenRemoveT...@talk21.com> 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. |
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14-05.-2008, 10:36 AM
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#24 |
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Guest
Posts: n/a
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Re: Polarized sun glasses
On May 14, 9:41*am, John Henderson <jhenRemoveT...@talk21.com> 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). |
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14-05.-2008, 12:24 PM
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#25 |
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Guest
Posts: n/a
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Re: Polarized sun glasses
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 |
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14-05.-2008, 12:51 PM
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#26 |
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Guest
Posts: n/a
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Re: Polarized sun glasses
On May 13, 7:36 pm, Don Mackie <ooo...@mac.com> wrote:
> On May 14, 9:41 am, John Henderson <jhenRemoveT...@talk21.com> 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. |
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14-05.-2008, 01:33 PM
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#27 |
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Guest
Posts: n/a
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Re: Polarized sun glasses
jobst.brandt@stanfordalumni.org 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! |
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14-05.-2008, 11:52 PM
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#28 |
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Guest
Posts: n/a
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Re: Polarized sun glasses
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. > |
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15-05.-2008, 02:44 AM
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#29 |
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Guest
Posts: n/a
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Re: Polarized sun glasses
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. |
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15-05.-2008, 01:19 PM
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#30 |
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Guest
Posts: n/a
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Re: Polarized sun glasses
On May 12, 10:20 pm, jim beam <spamvor...@bad.example.net> wrote:
> b...@mambo.ucolick.org 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/cata...optics/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 |
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