POLARIZED SUNGLASSES: IMPORTANT EQUIPMENT FOR OUTDOORS
Look at professional athletes competing in sports such as baseball, cycling, golf, fishing, shooting, skiing, tennis, track and field, beach volleyball, sailing… the list goes on. What do they have in common? Most of these athletes wear sunglasses. They are no longer an accessory rather a piece of equipment just as important as the rest of their uniform and gear. It ensures they can compete at their best without interruption or distraction. Sunglasses are an essential tool for optimum vision where split-second decisions mean the difference between winning and losing, or even preventing an accident. These athletes demand the most cutting-edge equipment in order to maximize their performance. Many utilize polarized sunglasses to help them succeed.
Because of their affordability, they can be used by everyone—even if you aren’t a professional athlete. The reason they are so popular is due to the increased visibility and performance they provide the wearer in everyday situations. While athletes use them to maximize their performance, the consumer can use them to maximize their experience. Whether it’s taking a relaxing hike, enjoying a casual Sunday drive, or relaxing with a book on a beach, polarized sunglasses can eliminate the distracting glare that causes visual discomfort in any sunny situation. Polarized sunglasses can best be described as a sun-glass option for many. Alpine EyeCare Center can fabricate a prescription polarized lens for you, too!
The light we see is electromagnetic radiation in the visible spectrum, 380 nm to 700 nm. Photons, the common unit of light, move in a specific speed in a specific direction but they also oscillate up and down along their path, giving them the properties of a transverse wave as well. Bundles of light reaching the earth from the sun oscillate at all angles, horizontal, vertical and everywhere in between. Some of this light lands directly on the eye, while some of it is reflected off of surfaces like roadways or water. This reflected light is slightly bent and scattered in all directions according to its angle of incidence on the reflective surface; some of these reflected light rays become polarized.
When a bundle of light hits a flat surface, it becomes polarized, i.e., is reflected only horizontally. It becomes concentrated and is blinding to the viewer. This intense reflection is commonly referred to as blinding glare. The reflections can be uniform, like light reflected off of the road ahead of a driver or from another car’s hood. The reflections could also be from non-uniform or changing surfaces, like running water or a non-uniform patch of ice on the road. No matter the case, the desired requirement is to filter out the distracting reflected light and provide a clear viewing experience for the wearer.
The properties of polarized filters are used in a variety of fields such as chemistry, engineering, professional photography, geology and astronomy. As an example, polarized filters can be used to highlight clouds for photographers or detect the amount of stress in lenses in a frame by observing the amount of bi-refringence (internal stress) induced. These properties can be exploited in a variety of engineering stress tests and is used in many finishing labs to ensure proper lens fit with minimal stress placed on the finished lens. One can think of polarized lenses as linearly aligned slit filters used to block incident light of a particular orientation. Think of the filter acting like Venetian blinds: The horizontal blind blocks incoming light from above and below. By blocking this light, it provides a clearer view when looking out a window; there are fewer distractions and reflections observed. For optimal viewing, a polarizing lens should stop horizontally polarized light from view while allowing vertical light rays through the lenses.
Another instance in which polarized lenses provide an advantage is while driving because of the elimination of glare from oncoming traffic or the road itself. Metallic and glass surface on other cars and the road itself can be quite reflective on bright days. This effect is amplified if it has recently rained or snowed. Suddenly, these surfaces are reflecting much more light and in many more directions. Polarized lenses filter and reduce the most intense horizontal reflections from these surfaces. The polarization keeps the wearer’s eyes relaxed and less strained, which can result from even a short drive.
DISADVANTAGES OF POLARIZED LENSES
Polarized lenses have never been suitable for aircraft pilots. The Federal Aviation Administration (or FAA) advises pilots against wearing polarized sunglasses because polarized lenses creating visible striations and decreased visibility when looking through aircraft windscreens. This visual noise (a colorful rainbow effect and visual obstruction) is not good for the pilot. Visibility is extremely important when spotting other aircraft in the sky or during high-traffic situations during takeoff or prior to landing. Polarized lenses effectively mask the sparkle of light from other aircraft, which in turn can hide their visible presence.
To the average consumer, the largest drawback is the disappearance or partial blackening of LCD screens like smartphones, car gauges, radio displays and gas pumps while wearing polarized sunglasses. LCD displays utilize a polarizer, placed at 45 degrees to ensure proper color contrast and clarity of the picture or often a circular polarizer. This isn’t a problem for the wearer when their lenses are aligned in a parallel orientation to the polarizer in the LCD screen. When the wearer is looking at an LCD device perpendicular to the polarizer, the image turns black. The same effect occurs if you hold two polarized lenses at 90 degrees to one another.
One other note of importance is that some skiers prefer tinted lenses instead of polarized lenses because of the reduced visibility of ice. Since the reflections are eliminated, skiers might not be aware of the ice until it is too late. Those competing in slalom events need to know where they have to check their speeds to safely take the corners. Although competitive skiers wear goggles for competition, many recreational skiers will wear their sunglasses and go straight from the mountain to their après-ski activities. This is another point of mention with patients who express interest in using their sunglasses on the mountain. I would strongly recommend a mirrored lens to reject a larger percentage of the very intense light a person can encounter when mountaineering, skiing, or other winter sports.
Despite these cautions, the advantages of wearing polarized sunglass lenses outweigh the disadvantages. It is important to consider lifestyle and overall use of the sunglasses to make the most appropriate decisions concerning patient lens selection. It is very important that these limitations are understood and easily explained by the dispensing optician for troubleshooting purposes or to discuss how polarized lenses will work for patients’ specific needs.
WHY POLARIZED LENSES?
The advantages to the wearer are a better visual experience during daytime activities. Visual noise such as the reflected short wavelengths of light are polarized and increase color saturation to the viewer by increasing edge contrast and color variations of an object. Environments look more vivid than if observed by the unaided eye: Leaves are a vibrant green, and the sky is a darker hue of blue. Because glare is almost fully blocked, polarized sunglasses provide visibility of an otherwise hidden object for the wearer. This can be important for spotting debris and road imperfections whether on a bicycle, motorcycle or while driving a car. The addition of anti-reflective coatings on the back surface of polarized lenses is the best for sunglasses. These coatings improve acuity by negating any ‘back-side’ mirror effect which can commonly occur on a darker surface. Think about the last time your walked past a dark glass office building during a sunny day and how the windows acted like mirrors. In competitive sports, back-surface reflections can get in the way of a critical decision leading to poorer performance or a loss of the event. As a cyclist, I know of the importance of the best optics while looking at the road for hours at a time. The visual demand is intense while scanning for debris and road imperfections while managing your position next to other cyclists—sometimes only inches away from you. Polarized lenses help to reduce this fatigue by filtering “noisy light” which can relax the eye.
SKIN AND EYE PROTECTION
Let’s not forget the general goal of sunglasses is to protect the eyes and the adnexa (the skin surrounding the eyes) from UVA and UVB light. All polarized filters are engineered to block these specific wavelengths of light waves regardless of the material of the lens. Any lens can be made to block UV light. Significant absorption is important for the health of the eye and ensures protection from damaging ultra-violet radiation that is associated with cataract development and retinal damage from prolonged exposure. Large sunglass frames act like a shield, protecting the eye and the sensitive skin around the socket. Sunscreen is used to protect the body from sunburn, so think of polarized sunglasses as sunscreen for the eyes. The protection from damaging UVA and UVB is necessary for anyone who spends a lot of time around water and snow. Due to the reflective nature of these environments, wearers are subjected to much more incident light radiation than those who vacation or infrequently visit these types of areas. This is also very important to consider at higher altitudes such as the Front Range communities like Boulder and mountains of Colorado where the UV and visible light is much more intense.
Sunglasses can protect the eye from low speed projectiles. According to the National Eye Institute, approximately 800,000 total eye injuries occur in the United States annually. Sunglass manufacturers purposely pair Trivex or polycarbonate lenses in sport frames for maximum protection. Large sport sunglasses wrapped close to the face can provide maximum eye protection in the event of an impact. Whether skate boarding, running, playing volleyball, trail running or participating in most any outdoor sport, the wearer can feel secure knowing that their eyes are protected from dust, debris and grit.
It is important to understand the advantages (and some disadvantages) of how polarized lenses will benefit the wearer. A high quality sunglass lens is crucial for optimal performance, maximizing your enjoyment and reducing visual strain. Alpine EyeCare Center would be happy to assist you with your customized needs – whether it is in a prescription or non-prescription sunglass. Come see us and take your sport, hobby or outdoor experience to a higher visual level!