MadSci Network: Physics

Re: I have polarized presciption sunglasses. How are they made?

Date: Mon Feb 9 21:14:42 2004
Posted By: Guy Beadie, Staff, Optical sciences, Naval Research Lab
Area of science: Physics
ID: 1076046101.Ph

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.

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

goes through a description of the various components of a sunglass lens.

This link

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:

This site describes some of the history and early polarization technology

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.

Current Queue | Current Queue for Physics | Physics archives

Try the links in the MadSci Library for more information on Physics.

MadSci Home | Information | Search | Random Knowledge Generator | MadSci Archives | Mad Library | MAD Labs | MAD FAQs | Ask a ? | Join Us! | Help Support MadSci

MadSci Network,
© 1995-2003. All rights reserved.