What Are Polarized Sports Sunglasses?
Sunglasses come in many shapes, sizes, and varieties. And when it comes to sports sunglasses, only the best optic design and technology can keep up with the demands needed to protect and enhance your vision for sports. There are several components that play a part in sports sunglasses: protective UV filters, glare eliminating polarized lenses, and comfortable, secure fitting wrap-around design. Each of these technologies is critical to protecting your eyes while offering the performance needed to optimize your vision during any outdoor sport or activity.
UV protection or protection against the sun’s ultraviolet rays is a fairly well understood and expected feature, but what about polarization? Polarized lenses are often a touted and sought after feature when it comes to sunglasses lenses, but few people know what polarized lenses do and even fewer understand how they actually do it. We’d like to shed some light on polarization so you can see the science behind your sunglasses.
What Do Polarized Lenses Do?
In the most basic of terms, polarized lenses eliminate glare, or light reflected off surfaces. The most noticeable and intrusive examples of glare are bright sunlight reflecting off of water when you’re fishing, glare off the asphalt when you’re driving, blinding white light reflecting off the snow on the ski slopes, and any time you find yourself squinting because the environment it too bright to accurately see the details of things around you. Polarized sunglasses use a polarization filter build into the lenses that blocks out reflected light before it enters your eye (we’ll get to how they do this in a moment), allowing you to see with enhanced contrast without squinting.
Polarized lenses can provide a number of sport-specific advantages, as well as better vision in general for any outdoor activity. Fishermen and boaters have been enjoying the perks of polarized lenses for years, as the elimination of glare on the surface of the water allows them to see what is swimming or sunken below. Better contrast can help hikers and joggers see paths in front of them more clearly, and improve the view along the way. Golfers can survey the golf course with greater attention to the details of the landscape, and hunters can benefit from improved contrast to help them spot any kind of game. Even in the car, polarized lenses give you a safer driving experience by blocking dangerous and hazard obscuring glare from the road.
How Polarization Works
We can all appreciate how polarized lenses help us to see even in the brightest conditions, but how do they do what they do? To understand how polarization works, you first need to know a little about how light, and more specifically how reflected light behaves. When light shines from the sun, the photons are emitted in a random manner in all directions; light waves vibrate in any variety of horizontal and vertical alignments. Reflected light has horizontal light waves that cause glare. Polarized lenses have thin a filter inside the polycarbonate which blocks these horizontal rays before they enter your eye, while still allowing vertical rays to pass through. The illustration below can give you a visual idea to better understand how reflected light behaves and how polarized filters block out glare before it gets to your eyes.
UV400 Protection
The most basic function of sunglasses is to protect your eyes from the sun’s harmful rays and make it easier to see. But not all sunglasses are created equal. Lenses for sunglasses have varying degrees of protection against ultraviolet rays from the sun. If you’re not careful, lower quality sunglasses can allow certain types of UV rays in and put your eyes in harm’s way.
Ultraviolet rays are measured in nanometers. When we talk about the sun’s harmful UV rays in regard to sunglasses, there are usually two kinds mentioned: UVB rays with a wavelength of 280-315mn, and UVA rays with wavelengths of 315-400nm. Some sunglasses only block out UVB or lower wavelengths of UV rays. Only sunglasses with a UV400 rating filter out UV rays of up to 400nm, offering 100% protection. Lower quality sunglasses may not even block most UV rays, so always check the UV rating to ensure quality. Many cheap sunglasses with little to no UV filtering will have darker tinted lenses, but don’t be fooled as darker lenses do not translate to UV protection.
Proper protection against ultraviolet light is of the utmost importance, especially to those who enjoy outdoor activities. Short term exposure to UV rays without eye protection can cause a slight burn to the front of the eye, similar to a sunburn on your skin. Over long periods of time, frequent unprotected UV exposure can cause clouding of your eye’s lens (cataracts), vision-obscuring growths in or around the cornea, and in some cases skin cancer around the eyes. For more information about protecting your eyes, take a look at the EPA’s “sunwise” information: http://www.epa.gov/sunwise/doc/eyedamage.pdf
Wrap-around Design
When you think of sports sunglasses, there’s one overall design that’s considered the standard: wrap-around. Plenty of sunglasses have polarization and UV400 protection, but traditional sunglasses are typically designed in a flatter shape for fashion more than function, and are intended for casual use. After all, humans have a round head, so a curved design naturally fits better. Only wrap-around sunglasses give a secure enough fit to keep up with sports and outdoor activities. Wrap-around design also offers improved protection against UV rays. Light that enters from the side of traditional sunglasses is called “stray light”. Wrap-around sunglasses have curved lenses and block light coming in from any and all angles.
