How Do Polarized Sunglasses Work?

In early times, sunglasses were barely useful for the purpose of keeping out the brightness of the sun. Bits of smoked quartz held by hand, and then later held to the face by a crude frame, they were hardly the practical fashion accessory that they have become today. Yet with the invention of the polarized lens, by Edwin H. Land, sunglasses went from keeping out the sun to keeping our eyesight healthy by blocking out harmful UV rays. To understand what a polarized lens is, we need to understand how polarized sunglasses work.
In the 1930’s the Army Air Corp approached a well known company, Bausch and Lomb, to research and develop an anti-glare style sunglasses for pilots. They came up with a design that made the frame slightly droop to maximize shielding of the pilots eyes. Then they incorporated a dark green tint which would absorb the yellow band of the light spectrum. The dark green tint filters and diffuses the concentrated light waves, which eliminates 99% of reflecting glare. The end result is a reduction of annoying and /or dangerous glare.
The way in which the polarized lens works to assist your sight is that it blocks the horizontally polarized light from a surface with a vertically oriented polarizer that is integrated into the lens. Surfaces such as still water, flat pavement, or even glass and shiny metals can reflect a large amount of light into the eyes which makes it difficult to focus properly on the surface and the items around it. This can cause a person to be distracted or even not see items that become hidden behind the bright light. Using polarized sunglasses removes the glare by bouncing it off your sunglasses allowing you to actually see through the glare.
Sometimes polarized lenses may react poorly with LCD (liquid crystal display) lighting commonly found in car dashboards or on bank machine displays at automated tellers. In fact, depending on the angle of the screen display, the LCD display can become almost invisible. This is of course is something that needs to be explored before sitting behind the wheel of your car.
Polarized sunglasses are no longer just for pilots or drivers. They are now part of an ever growing group of sports enthusiasts for many types of sports events including many outdoor winter activities such as skiing. However, polarized lenses sometimes do not work well on reflective snow surfaces, so be sure to try out the sunglasses you plan to use for your outdoor snow day activities.
A Test for Polarized Lenses
If you wish to test your sunglasses to make sure they are actually polarized, find a surface that is reflecting a large amount of light such as a still lake on a sunny day. Find the brightest or most reflective part of the lake’s surface, and then put on your polarized sunglasses and look at the same area of the lake. While looking at the spot, turn your head to the right and left observing any differences. If you see that the lens gets light and then dark or, that there is a significant reduction in the glare, you have confirmed that your sunglasses are polarized.
There are also polarized photo-chromic lenses now on the market that are capable of changing the amount of light they let in. This is a great asset for people who are frequently in and out of shaded areas or in and out of buildings during the course of the day.
With the increased health risks associated with UV rays, polarized sunglasses are a healthy choice for everyone.