Polarized sunglass lenses have a special filter within the lens that reduces glare better than conventional sunglasses.  This glare-blocking feature makes polarized lenses the perfect choice for activities where reflective glare can be a problem - such as driving, boating, and fishing.

The History (and Physics) of Polarized Lenses

Sunlight consists of light rays that radiate outward in all directions.  When sunlight strikes a flat surface - like a body of water, a sheet of glass, pavement, sand, or snow - some light rays are reflected.  The smoother and flatter the surface, the brighter the reflections can be.

Reflected light is partially polarized, meaning that the light rays are traveling in a more aligned, less random fashion.  In 1929, Edwin Land was a freshman at Harvard University.  Land came up with the idea of embedding tiny crystalline materials in a thin, transparent plastic film to create polarized light.  He patented this first sheet polarizer the same year, calling it the J sheet, and later, Polaroid. 

In 1937, Land established the Polaroid Corporation in Boston.  Thus the word "Polaroid" was born.  To this day, polarized lenses made by other manufacturers are sometimes (mistakenly) called Polaroid lenses.

Because Land's polarizing film could block light rays that were radiating in one direction and allow other light rays to pass (if they were radiating in a direction that was rotated 90 degrees from the blocked rays) it was very effective at filtering reflected light. 

Land's original idea was to add polarizing filters to the headlamps of cars to reduce glare for drivers and increase the visibility of pedestrians crossing the street.  But auto manufacturers were unwilling to adopt his idea. 

It was one of Land's colleagues who discovered the value of the Polaroid filter for sunglasses.  Shortly after Land's idea for polarized auto headlamps was rejected, a coworker took a scrap of Polaroid with him when he went fishing.  He returned with a large trout and explained to Land that the polarizing filter eliminated glare from the surface of the water, enabling him to better see fish in the stream.  Soon afterward, Polaroid sunglasses were sold in sporting goods stores across the country.  Since then, polarized sunglasses have become popular for driving and other outdoor activities when reflective glare may be a problem.

Today polarized filters are used for a number of applications beyond sunglasses - including contrast-enhancing camera lens filters and anti-glare screens for computer monitors.

How to Know If Sunglass Lenses Are Polarized    

Polarized sunglass lenses look the same as regular sunglasses.  The thin plastic polarizing film is embedded in the middle of the lens material and is essentially invisible. 

To determine if sunglasses have polarized lenses, perform this simple test:

1.      Find an object with a flat surface that is reflecting light (such as an auto windshield or a glass countertop). 

2.      Hold the sunglasses a few inches from your face so you are viewing the object through one of the lenses.  The reflections from the object should be reduced significantly.

3.      Now rotate the sunglasses 90 degrees (so the temples are located at the top and bottom of the lenses).  When held in this position, the polarizing filter in the lenses allows more of the reflected light to pass through the lens and therefore reflections from the object are more visible.

4.      If the sunglasses have regular (non-polarized) tinted lenses, there will be no difference in the amount of reflections from the surface of the object as the lenses are rotated.

When Polarized Sunglass Lenses Are The Best Choice

Though polarized sunglasses are an excellent choice for general outdoor use, they are especially recommended for the following activities:

• Boating - Polarized lenses enable you to see possible obstructions under the surface of the water.  They also reduce glare and eyestrain from reflections from the water's surface.

• Fishing - As Edwin Land's colleague discovered, polarized lenses help you locate fish under the surface of the water.

• Driving - Polarized lenses reduce glare from light reflecting off your dashboard and hood and the windshields and bumpers of other vehicles.

• At the beach - Even sand reflects sunlight.  Polarized lenses reduce eyestrain from light reflecting off both the sand and the surf.

• Skiing - Snow is highly reflective.  Polarized lenses cut glare from the surface of the slopes and trails.

When Polarized Lenses May Pose a Problem

For certain activities, polarized lenses are not the best choice:

• Skiing in icy conditions - Patches of ice will reflect more light than snow.  Wearing polarized lenses can make icy patches more difficult to see.

• If your car windshield is polarized - The windows of some automobiles are partially polarized.  Wearing polarized sunglasses may make an interference pattern of light and dark spots visible in the windshield.

• Viewing liquid crystal displays (LCDs) - Polarized lenses can make the liquid crystal displays of certain objects - like ATM machines - more difficult to read.