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Medical Forum / General / Vision / November 2005Testing sunglasses for UV protection
Hey, all. I recently bought a pair of nice Serengeti sunglasses off Ebay. The price was _really_ good - like less than 40% of retail. It was cheap enough for me to wonder if they might be a knock-off. The build quality seems really good; the only thing that would bother me about them not being 'real' Serengetis would be the actual quality of the UV protection they offer. I understand the issue about sunglasses with bad UV being worse for your eyes than not wearing anything, because they cause your pupils to dilate and let in more UV that way. Is there a home-brew way I could 'test' the UV protection of these things? Maybe some test involving chemical reactions to UV light of some compound I could lay my hands on? Thanks!! BD > Is there a home-brew way I could 'test' the UV protection of these > things? Maybe some test involving chemical reactions to UV light of > some compound I could lay my hands on? Dark-tinted plastic lenses are pretty good UV filters, even without coatings. It's hard to tan under most any sunglasses. If you need more reassurance, many opticians have a UV meter for demonstrating UV transmittance. The difference between 10% and 0.1% isn't often important. -MT >Dark-tinted plastic lenses are pretty good UV filters, even without coatings. Interesting; that's pretty much opposite of views I've read which prompted me to ask the question. I think the argument is that UV light is not affected by dark tinted lenses, at least not to the same degree as visible light; the net effect is that if you're behind dark lenses, your pupils open up, and let in an inordinately large amount of UV light, which can basically mean that 'bad' sunglasses can be worse for you than no sunglasses at all. Oh well. Interesting regardless. I may call an optician and just see if they can test the approximate UV protection of the lenses I have. > >Dark-tinted plastic lenses are pretty good UV filters, even without > >coatings. > > Interesting; that's pretty much opposite of views I've read which > prompted me to ask the question. Depends on who's selling what, in my experience. > I think the argument is that UV light > is not affected by dark tinted lenses, at least not to the same degree > as visible light; the net effect is that if you're behind dark lenses, > your pupils open up, and let in an inordinately large amount of UV > light, which can basically mean that 'bad' sunglasses can be worse for > you than no sunglasses at all. It was a popular urban legend ten years ago. But the math doesn't work. The amount you dilate behind sunglasses (say, from 4 mm to 6) might double or triple the UV flux through your pupil. But plain old dark CR39 reduces UV by 90 or 95%. Of course all UV wavelengths aren't filtered equally. The optician's meter will test mostly for UV-A because UV-B and C are generally blocked by anything. -MT >The amount you dilate behind sunglasses (say, from 4 mm to 6) might double >or triple the UV flux through your pupil. But plain old dark CR39 reduces UV >by 90 or 95%. Oh, okay - well, if that's the case then I just won't sweat it at all. Thanks for the reassurance! > Hey, all. > [quoted text clipped - 16 lines] > > BD All sunglasses by law must have UV protection. That is no guarantee, but it is unlikely that it lacks the UV protection you want. I think it is harder to find glass or plastics that are not UV absorbant.  SignatureLater 'gator NOSPAMddlee10@hotmail.com remove NOSPAM for email > Hey, all. > [quoted text clipped - 16 lines] > > BD |
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