Sunglasses, Sun Glasses, Sun-Glasses…All About Sunglasses
Sunglasses help us while most of us spend a large portion of our lives involved in outdoor activities, whether it’s driving down the highway, playing golf or strolling down the street. The world we see, or perhaps don’t see, depends upon the type of sun glasses lenses we are or are not wearing. Much of that world is outdoors and requires some special viewing consideration.
True sunglasses lens performance, in addition to good looks and relief from brightness, must also include the following: VLT—Visible Light Transmission, which is the percentage of light transmitted by a sunglasses lens. The lower the transmission the darker the sunglasses lens. This value is an “average” of all the wavelengths being transmitted.
In this article we explore several consideration regarding your choice of sunglasses. It is not enough to just buy sunglasses that look good. You need to consider deeply how you will be using the sunglasses, special considerations for the choice of sunglasses lenses, and whether it is better to use prescription sunglasses or regular plano sun glasses lenses.
Though invisible to the human eye, ultraviolet light presents risks to the delicate skin around the eyes by the contributing to the formation of premature wrinkles and various cancers, as well as to the tissues of the eye itself. Prolonged unprotected exposure can lead to ocular damage in the form of burns, pingueculas and pterygiums, as well as the increased risk of cataracts and macular degeneration. It is law in the United States that all sunglasses must have UV protection.
Like UV, infrared radiation (IR) is invisible. It is the longer wavelength after the visible color red in the spectrum. Infrared radiation creates heat. Dyed plastic sun glasses lenses have poor infrared absorption while green glass sunglasses lenses absorb IR. Infrared protection may be obtained through the use of mirror coatings on sunglasses.
Blue Light/Short Wavelength Control
The visible spectrum is the range of wavelengths our eyes see and blue light is the short wave length part of that spectrum. They are readily scattered by dust or the moist atmosphere of haze, fog, smog or rain. When blue light is scattered, it does not come to focus on the retina.
This condition is sometimes referred to as “blue blur.” With a portion of the visible spectrum in focus and a portion out of focus, overall vision lacks contrast and clarity. A sunglasses lens that absorbs the blue end of the spectrum will prevent the scattered light from interrupting a clear focus. Brown, amber, melanin, yellow and red sun glasses lenses absorb blue light and are called high contrast.
Safe Sunglasses Lens Material
While good quality sunglasses are available in all sun glasses lens materials from glass to polycarbonate, it is important to note many outdoor activities involve more aggressive action.
As the activity level escalates, your choice of sunglasses lenses should incorporate greater levels of impact resistance into the lenses. A glass sun glasses lens for fishing in a stream is fine, but for competitive sports like baseball, lacrosse and field hockey a more impact-resistant sun glasses material like polycarbonate , Trivex or NXT would be a better choice.
Elimination of Glare on Sunglasses Lenses
Overly bright may be a nuisance, but blinding glare can be dangerous. Glare results in a loss of visual performance, which is produced when an object or light source in the field of vision is brighter than the amount of light to which the eyes are adapted. Most tinted sunglasses lenses will provide some absorption to dampen brightness, but only a polarized sunglasses lens can effectively eliminate blinding glare. According to insurance statistics there are 18,000 car accidents in this country every day with as many as 6,000 of those accidents directly attributable to over- brightness and glare. Drivers are particularly vulnerable to the hazard of blinding glare. The modern style of today’s streamlined and slanted windshields in combination with the exterior matched lighter colored dashboards can create intense glare that can cause temporary blindness leading to tragedy in a moving vehicle. Drivers need much more than simple sunglasses protection against annoying brightness.
Clear Acute Vision
If sunglasses lenses are tinted too dark, the resulting decrease in light transmission will cause a lowering of visual clarity. Behind dark lenses the wearer’s pupils enlarge to gather more light but reduce depth of field. Polarized sunglasses lenses block excessive light and glare enabling sun protection with sharpness and clarity.
Perhaps the most overlooked characteristic of a quality sunglasses lens is its ability to improve visual performance by enhancing contrast sensitivity through the use of color filters. Contrast sensitivity in a sunglasses lens is the ability to distinguish between an object and the viewing background. If the general use and type of activity are analyzed, selective use of colored sunglasses lenses can enhance the wearer’s ability to react and perform at a higher level. The average consumer may get average protection from any pair of sun glasses, but if you provide contrast enhancement for a particular sport then the sunglasses lenses will meet higher performance needs.
--Article reprinted from 20/20 Magazine with permission from Jobson Publishing.