|MadSci Network: Physics|
Different companies use different techniques and different materials to polarize the light that comes through polarizing sunglasses. Your best bet for determining exactly how your lenses have been constructed, and how to handle them, is to go to the manufacturer’s website. If it’s not explained there, then you ought to at least be able to get a phone number of someone you could call directly. With that as a specific, but not immediately helpful answer, I will now feel free to speculate on how your glasses are polarized and how you should handle them. HOW SUNGLASSES ARE POLARIZED The polarization properties of your lenses is almost certainly due to a thin layer of material made up of organic molecules (poly-vinyl alcohol) that have a specific linear orientation to them. These molecules will absorb most horizontally-polarized light when the you’re wearing the glasses normally. This film is easily damaged out in the open, but it will definitely be an inner layer of the many layers that make up your lens. It may be sandwiched between two pieces of glass, or it may be on the outside of a single piece of glass but underneath a scratch-resistant coating applied to the outside of the lens. This site http://travel.howstuffworks.com/sunglass4.htm goes through a description of the various components of a sunglass lens. This link http://www.technical-gear describes a specific lens design, showing all the different layers that make up their high-end shades. This is a sunglasses company FAQ, addressing some common questions concerning specialty lenses: http://www.actionoptics.com/faq/frameMainFAQ.html This site describes some of the history and early polarization technology http://www.bruneni.com/Polarized/PolarFrameset.html?=polar01.html HOW YOU SHOULD HANDLE YOUR SUNGLASSES Unless you have very inexpensive (or poorly-designed) sunglasses, the lenses should be coated with a scratch-resistant layer. While not scratch- proof, these layers will protect your glasses from most wear and tear. You ought to be able to wipe them clean with most soft, CLEAN fabrics, and soap & water will work perfectly for fingerprints. HOWEVER, be careful when cleaning your lenses. Rubbing a cloth over the lens is not the problem: trapping a little piece of sand or grit between the cloth and your lens is. Even a scratch-resistant coating will fare poorly when you scrape a piece of sand over it. Don’t use a T-shirt or towel to clean them if you’ve been out to the beach. And if your glasses already have sand on them, be sure to rinse them with water before wiping them clean. Lens companies are eager to sell you lens cloth. The advantages are that the cloth is very soft, has no lint to leave behind, and if you have it you will likely keep it in a protected pocket which will keep it clean. In my estimation, however, the cost is rarely worth it. The scratch resistant coating is more than proof against cotton or other common materials, so you won’t see a problem unless you rub really hard for a very long time. Though other materials may leave some lint behind, you can usually wipe in such a way that this is minimized or even non- existent. Finally, the cloth doesn’t protect against the primary problem with cleaning glasses: sand and grit. The cloth may be kept clean in a protected place, but you can find other clean cloths almost anywhere (napkin, towels, clean T-shirt, etc.) And no matter how clean you keep your lens cloth, if you don’t rinse sand off your lenses before wiping they’ll get scratched just as easily as with a T-shirt.
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