The removal or decrease of sunlight (ultraviolet A and B rays) entering the eye from the top of the sunglasses frame or from the sides is a crucial component when fitting sunglasses. Finding a lens shape that completely covers the “eyes” is crucial because everyone’s facial structure is different. A lens’s “base curve” is the amount of curvature at the front of the lens. You’ve probably noticed that the sunglasses frame has a much more aggressive curvature than reading glasses does in order to accommodate the curved lens. Larger base curves indicate more curved lenses that wrap around the face to protect the eyes. Whereas typical sunglasses have an 8-based base curve, reading glasses have a zero-based curve.
Frames for sunglasses are available in a range of widths. A frame that is too wide will enable top and side ambient light to penetrate. On the other hand, a frame that is excessively tight can feel uncomfortable after a while. When wearing sunglasses, most people prefer a lighter weight and feel; normally, weight is influenced by the material of the frame and lenses as well as their thickness. A qualified eyewear expert will assist in ensuring proper fit. Horizontal (temple to bridge) and vertical measures are the two most important fitting parameters (measurement or the height of the lens).
Four Primary Ingredients for Lenses
To assess the optical clarity of lens materials, two metrics are used. Abberation, also known as the Abbe value, and Index of Refraction, a ridiculously complex measurement that takes into account ultraviolet wave length velocity, light refraction (the bending of light), and the dispersion of refracted light through various lens materials. The higher the value, the clearer the optical system. Abbe value will be used in this context to define optical material clarity.
Abbe value for glass is 59. Superior in terms of optics, but heavy and liable to break on impact.
Abbe value for polycarbonate is 30. Although polycarbonate has been the industry standard for 30 years, it has the highest amount of distortion unless the lens is optically corrected (the center is ground thinner than the lens perimeter to minimize distortion). In general, polycarbonate is lighter and thinner than CR-39.
Abbe value = 58 CR – 39. Optimally superior hard resin that is thicker and heavier than polycarbonate.
Abbe value = 43–45 for High Index Materials (NXT – Trivex). More pricey than polycarbonate or CR-39, however incredibly light, robust, and durable. Photochromatic lenses, often known as transition lenses, are also gaining popularity since they change color as the light level varies.
Distortion occurs when lens materials are heated and bent to fit particular eyeglass frames. Lenses are “center ground” or “de-centered,” which means they are often thinner in the center and broader around the lens periphery, to optically rectify this feature. Aspheric lenses are another name for optically correct eyeglass lenses.
Sunglasses are subject to FDA regulation in the US, and the Office of Ophthalmic Devices classified all sunglasses as Class 1 medical devices. Testing is done to determine the transmission of UV light through the lens under strict requirements. All imported sunglasses must contain proof of testing and an indication of the country of origin on the arm. Moreover all sunglasses must prove impact resistance in a “drop ball” test.
Polarization: A Polaroid invention
Glare is considerably reduced by polarized lenses. Polarized film is either injected into the lens material or sandwiched between two pieces of the selected lens material. Because the horizontal filament allows the vertical light rays to flow through the lens while blocking the horizontal light rays from entering the lens, glare is reduced. Glare from water or a road surface is considerably diminished, if not completely removed, if light travelling through the lens only goes in one direction. Brightness and glare are two distinct factors that must not be mixed up. Polarization’s only drawback is that it frequently isn’t recommended for usage in aviation because it may affect how instruments are seen. Using polarized sunglasses while using a bank ATM may cause screen distortion. Non-polarized sunglasses account for just 10% of our total sales.
Frame Components
Sunglasses with plastic frames are inexpensive and frequently include plastic lenses that have not been decentered or optically adjusted. Often, plastic sunglasses retail for $15 or less.
TR-90 This polymer is incredibly flexible and much more heat resistant than plastic, making it far more resilient in the event that sunglasses are left in a warm car.
Aluminum, Composites, Wire, and Magnesium Heat won’t change the contour of the frame; it is lightweight but strong. more expensive than sunglasses with TR-90 frames, on average.
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Tinting lenses
While most tinting is aesthetic, the right hue, which is influenced by the light, may improve eyesight. It is advised to use two tints. All colors are transmitted uniformly without modifying the value of color in the first gray or smoke (darker). Second, brown or amber can reduce the amount of blue light that is present when it is cloudy or overcast outside. For continually bright situations, darker lens tints are typically advised; overcast days may be better suited for a brown or amber lens.
Optical Coatings
The feature known as Anti Reflective Coating (AR) is present in more expensive sunglasses. UV rays may bounce from the interior of the lens and direct UV rays back to the eye if ambient light enters skin through the corners of the sunglasses or from above the frame. The front and rear of the lens include an AR coating for glare reduction in the most efficient AR systems. AR coatings on the backside stop UV rays from bouncing back into the eye.
The anti-scratch
The lens becomes more scratch-resistant thanks to this coating. While any lens will eventually scratch, this usually happens to the coating rather than the actual lens. Scratches can occasionally be removed by polishing by an optician.
In outdoor recreation settings, anti-fog coating, rain X, or water-resistant coating could all be quite helpful.
Body Hinges
Stainless steel hinges are attached to the sunglasses arm and frame with adhesive, and the sunglasses arm is fastened to the hinges of the frame with screws. Stainless steel hinges are typically less robust than pin hinges, which are pins put between the sunglasses arm and frame hinge.
Head Bridge
The sunglasses won’t “slide,” which happens when moisture accumulates in hot weather due to perspiration, with the help of an elliptical hydrophilic nose pad.
A hydrophilic (waterproof) coating substance should also be used on the temple pads and arm tips.
Care
Cost versus utility are often considered when making any kind of purchase. When a consumer spends $200 or more on a product, losing or damaging costly sunglasses is upsetting. Avoid contacting the sunglasses lens with your fingers whether putting them on, taking them off, or cleaning them. Oils could harm the lens coating. The majority of manufacturers include a microfiber polishing cloth for cleaning. Again, some cleaning agents and glass cleaners may be detrimental to lens coatings, so simply washing the lens with water will do. Never use paper products to clean or dry the lens since they are extremely abrasive. As little as possible should be bent at the arm of the sunglasses. A $10 investment in a hard case for protection or a floating restraint strap might be a smart move that helps to increase the lifespan of your sunglasses.
