Many styles of sunglasses are available with polarized lenses. This type of lens is popular with those who play outdoor sports, those who drive a lot, and people who spend time on boats or fishing. The reason people choose polarized sunglasses is because the lenses selectively cut down on glare from horizontal surfaces like water, playing fields, and the hoods and roofs of vehicles. Polarized lenses allow people to see more clearly when there is glare off horizontal surfaces, reducing eye strain and making hazards easier to see. Polarized lenses don’t dim the field of vision, so whether lenses are polarized or not is unrelated to how dark the lenses are.
Unpolarized vs. Polarized Light
Unpolarized light waves move in all different directions. Polarized light waves, however, move in a more orderly fashion. Polarized light waves are oriented in the same direction. If you have a pair of polarized sunglasses, you can see the effects of polarization by rotating the glasses 90 degrees, so they’re going up and down rather than side to side. At this angle, you’ll see glare off horizontal surfaces. But when you orient polarized sunglasses normally, as they are when you wear them, glare is reduced or eliminated. If you have two pairs of polarized sunglasses and rotate one pair, while holding the other in a fixed position, you’ll notice that almost all light is blocked. You can also get this effect by rotating a polarized lens in front of a flat screen monitor, as shown in the animation below.
Animated polarizer in front of a computer flat screen (Image Wikimedia Commons)
(animated version is at http://upload.wikimedia.org/wikipedia/commons/5/54/Animation_polariseur.gif)
How Are Light Rays Polarized?
Some naturally occurring crystals polarize light, but polarized sunglasses are created by using special lenses designed to block horizontally polarized light. First, polarized film is made from a material called polyvinyl acetate, or PVA, which is similar in thickness to the plastic wrap you use in the kitchen. The PVA is heated and stretched, which causes the chain molecules that make up the PVA to align. When the stretched, heated film is dipped into an iodine solution, the molecular PVA chains create long, parallel darkened lines that the unaided human eye cannot see. These lines block horizontally polarized light. The processed PVA is placed between two sheets of a material called cellulose acetate butyrate, or CAB, and this is affixed to the lenses of polarized sunglasses.
Disadvantages of Polarized Lenses
There are some people who should not wear polarized sunglasses, because they can block shadows that provide critical visual information people need for safety reasons. Advanced skiers and snowboarders should avoid polarized lenses, for example, because polarized lenses can make it harder for them to distinguish a small jump from a large hole due to blockage of shadows. Motorcycle riders should avoid polarized lenses as well, because they can make it more difficult to distinguish wet and dry pavement. Also, polarized lenses can make it hard to read liquid crystal displays, like the ones on gas pumps, but if you tilt your head, you can make up for this effect.
Who Can Benefit from Polarized Sunglasses?
Those who participate in outdoor activities like boating, fishing, golf, tennis, or baseball can benefit from polarized sunglasses. If you drive long distances, polarized sunglasses can reduce eye strain and improve visibility by reducing glare off your windshield and other cars. Some people who have had cataract surgery are advised to wear polarized sunglasses due to increased light sensitivity.
Check out our most popular post: POLARIZED VS. NON POLARIZED SUNGLASSES
This is a little test we did and although it’s a test that is really to be done in person, we put it on video to see if it can try to simulate over video.