Recently I made a trip to California to see our children and grandchildren. We spent some time in the area from LA to Santa Barbara. As we visited the areas mentioned I began to notice that the majority of people spend more money on shoes and sunglasses or hats than on the rest of the clothes they wear. At least it looks like they do. The experience got me to thinking about sunglasses and the money we all spend on the product lines. Where is the value? What is being protected? What do the glasses do and not do? How much do we need to spend to be cool?
Visible light is composed of waves of electromagnetic energy. The light waves are of variable lengths. Those with the shortest lengths have the most energy. Ultraviolet rays are at the short end of the visual light spectrum and are richly present in natural sunlight. Because of the high energy they carry, UV light waves can damage both the cornea and retina of your eye. Therefore, sunglasses should try to protect our eyes from 100 percent of the incoming UV waves.
Different from UV damage is the problem of glare. Glare is the intensity (the brightness) of the sum of the natural visual light we encounter. At a certain intensity, glare will begin to distort our vision. We notice this looking directly into bright sun, or during night driving with oncoming headlights. The natural reaction is to squint to reduce the brightness, but prolonged exposure to extreme glare can result in temporary, or rarely permanent blindness.
Thirdly, reflected light, usually from a flat surface such as the surface of water, will increase the intensity of observed light. We recognize this when we try to look through the surface of a body of water, or squint when we encounter glare from the wet road surface reflecting oncoming headlights. Direct sunlight approaches the eye from all directions and planes. In contrast, reflected light is restricted to one plane or direction of impact. As a result, rather than tint which limits all direct visual light, sunglasses can use a polarizing filter which will block light approaching from the most likely plane of reflection, usually just off the plane of horizontal. Such polarization allows for light not in the horizontal plane to enter the eye, improving vision in some situations such as looking for that trophy snook cruising the flats.
While lens tinting and polarization both modify the impact of visible light, Ultraviolet light waves outside the visible light spectrum must be handled separately. UV light is reflected by the lens itself (the windshield of your car does this). Quality sunglasses should reflect 100 percent of the damaging UV waves. This property of the lens should be clearly stated on the packaging.
The quality of vision through sunglasses is affected by the quality of the glass or polymer (plastic) used for the lens. High quality glass and plastic both produce excellent lenses. Plastic is lighter and glass is less likely to scratch. The choice of color tinting can accentuate certain color contrasts and attenuate others. Shades of grey tinting to reduce glare seem to provide the best color fidelity, for instance. Depending on what the sunglasses are used for, you may choose a flat lens for accuracy of object identification or distance, or a curved lens which provides better protection from light scatter but may produce some distortion of the visual field.
In summary, looking cool is fine. Spending $50 or $500 can make you cool. For everything else, however, there are choices to be made. Ask yourself what the sunglasses will be used for. Where possible, maximize UV and glare protection. Choosing high quality glass or plastic lens will provide better visual fidelity, but are more expensive. Unfortunately, using rose-colored glasses doesn’t help with vision, but may make things seem better.
Lastly, sunglasses will not protect you from Covid-19. Please get vaccinated, wear a mask if not vaccinated, and socially distance when appropriate.