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Medical Forum / General / Vision / January 2007polarized sunglasses
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 >I bought a quality pair of polarized sunglasses (Hobie, $60 sale/$160 > retail) for driving purposes, especially to help in daylight rainy [quoted text clipped - 20 lines] > > 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. > 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. > 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 > 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. Yes, I suspect the Hobie sunglasses are designed glare coming off the water, not straight in front of you. Hobie started out as a watersports company making surfboards and small sailboats. On 1/28/07 11:50 PM, in article 1170057000.658437.227290@s48g2000cws.googlegroups.com, "Bucky" <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. > 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. > 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. > 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. > http://www.hobiepolarized.com/eyewear.aspx Bill -- Fermez le Bush--about two years to go. > <uw_badgers@email.com> wrote: > [quoted text clipped - 7 lines] > 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.  SignatureCheers, 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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