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Medical Forum / General / Vision / August 2005MSNBC said polarized lenses do not block UV rays
MSNBC said polarized lenses do not block UV rays. They did a survey in which inexpensive sunglasses, down to $2, all blocked at least 99% of the UV rays. I checked with a few web sites and they sell polarized sunglasses that also do UVA and UVB blocking. Should I assume that polarized glass does not block these rays but the manufacturers simply ad a coating as a final process? Thanks, Gary Polarization and UVa/UVb protection are mutually exclusive. Plano glasses sold commercially as sunglasses are required (in the US) to provide UVa/UVb protection. Polarization is accomplished by adding something (chemical, maybe?) to the lens material, casting the lenses, then treating the lenses with some other chemical to activate the first. Or such is my understanding. I'm sure someone with more accurate information will weigh in. >MSNBC said polarized lenses do not block UV rays. They did a survey in which >inexpensive sunglasses, down to $2, all blocked at least 99% of the UV rays. [quoted text clipped - 6 lines] > >Gary +++++++++++++ Reply to the list as I do not publish an email address to USENET. This practice has cut my spam by more than 95%. Of course, I did have to abandon a perfectly good email account... What is UVb? > Polarization and UVa/UVb protection are mutually exclusive. Plano > glasses sold commercially as sunglasses are required (in the US) to [quoted text clipped - 22 lines] > This practice has cut my spam by more than 95%. > Of course, I did have to abandon a perfectly good email account... > What is UVb? The "ultraviolet" part of the solar light spectrum is divided into three wavelength bands, A, B and C. UV-b is the wavelength which can cause sunburns, tanning, skin cancer, cataracts and other tissue changes. "UV" and the wavelength cut off that calls one A and one B is just a number. The damage caused by the rays does not pay attention to the numbers and it is clear that the shorter the wavelength (C being the shortest and deadly to living things), the more risk of damage to living tissue. Think of C as catastrophic, B as bad and A is less bad approaching alright and visible. LB, O.D. That explains so much about UVa and UVb. Is UVc blocked by all glasses. I can't recall ever seeing it advertised. > > What is UVb? > [quoted text clipped - 10 lines] > > LB, O.D. > That explains so much about UVa and UVb. Is UVc blocked by all glasses. I > can't recall ever seeing it advertised. UV-c is blocked by the earth's atmosphere-----better be careful about protecting it or we all become extinct. --LB, O.D. > Polarization and UVa/UVb protection are mutually exclusive. Plano > glasses sold commercially as sunglasses are required (in the US) to [quoted text clipped - 5 lines] > Or such is my understanding. I'm sure someone with more accurate > information will weigh in. You're attempting, I think, to describe photochromic lenses---a material that changes darkness upon exposure to UV energy. But incorrect in any event. As is the information presented at MSNBC. Polarized lenses can be made of glass or plastic, both materials will inherently block UV/b energy and most polarizing lenses block UV/a as well. Polarizing lenses consist of two layers of glass or plastic with a polarizing plastic layer in between as a laminate or two single layers bonded together. Horizontally reflected light is "cancelled" nearly 100% and as such there is complete blocking of all light, including UV. Light at other angles is reduced by the absorption level of the material, usually 75-90% and UV is blocked accordingly or at even high levels depending upon the material or applied coatings. --LB, O.D. these are two different things. polarized lenses might very well not block UV light. On 8/8/05 11:20 AM, in article VnNJe.4098$lK2.284@trndny01, "Gary" <GParent@rocketmail.com> wrote: > MSNBC said polarized lenses do not block UV rays. They did a survey in which > inexpensive sunglasses, down to $2, all blocked at least 99% of the UV rays. [quoted text clipped - 6 lines] > > Gary There is nothing intrinsic to polarized film of the Polaroid type that would make them UV blocking. On the other hand, many materials do block UV and I am pretty sure that nothing is purposely done to avoid such materials. Even the polarized glasses I have bought at the 99¢ store were claimed UV blocking. I'd be a bit more wary of glasses coming from China or any third or fourth world country. Bill >MSNBC said polarized lenses do not block UV rays. They did a survey in which >inexpensive sunglasses, down to $2, all blocked at least 99% of the UV rays. [quoted text clipped - 6 lines] > >Gary Gary, Polarized Gray C crown glass blocks 96.5% of the UVB and 84.5% of UVA. That should be enough protection for mid and northern latitudes at or near sea level. This lens can not be tempered so that the lens can crack easily if dropped. Polarized CR39 plastic blocks 100% of the UVB and UVA. Transmittance at 400nm is less than 5%. Hope this helps Robert Martellaro ~~~~~~~~~~~~~~~~~~ Optician/Owner Roberts Optical robopt@execpc.com ~~~~~~~~~~~~~~~~~~ "An expert is a person who has made all the mistakes that can be made in a very narrow field." - Niels Bohr |
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