In the hot summer days, most of the people will wear sunglasses to protect their eyes from the strong sunlight. In the very beginning, the main color of the sunglasses lens is black, which is almost the symbol of gangsters when in the movies.
Now people have more choices when choosing the sunglasses according to their preference. But few people know how to choose the right sunglasses, or rather the right lens.
Lens are the main component in the sunglasses, and its color decides what to what extent it will protect our eyes. The color of the lens can vary depending on style, fashion, and purpose, but for general use, red, grey, yellow, or brown are recommended to avoid or minimize color distortion which could affect safety when, for instance, driving a car or a school bus.
Gray and green lenses are considered neutral because they maintain true colors
Brown lenses cause some color distortion, but also increase contrast.
Turquoise lenses are good for medium and high light conditions because they are good at enhancing contrast, but do not cause significant color distortion.
Orange and yellow lenses increase both contrast and depth perception. They also increase color distortion.
Yellow lenses are used by pilots, boaters, fishers, shooters, and hunters, for their contrast enhancement and width perception properties.
Blue or purple lenses are mainly cosmetic.
With the introduction of office computing, ergonomists, may recommend mildly tinted glasses for use by display operators, in order to increase contrast. Clear lenses are typically used to protect the eyes from impact, debris, dust, or chemicals. Some sunglasses with interchangeable lens have wet lenses to protect the eyes during low light or early morning activities.
While some blue blocking sunglasses (see above) are produced as regular sunglasses for exposure to bright sunlight, others—especially for macular degeneration patients—do not block light or other colors in order to function well in regular daylight and even dim sunlight.The latter allow the passage of enough light so normal evening activities can continue, while blocking the light that prevents production of the hormone melatonin. Low-tinted blue glasses are sometimes recommended to treat insomnia; they are worn in artificial lighting after dark, to reestablish the circadian rhythm. Some models have polarized lenses, made of Polaroid polarized plastic sheeting, to reduce glare caused by light reflected from polarizing surfaces such as water (see Brewster’s angle for how this works) as well as by polarized diffuse sky radiation (skylight). This can be especially useful when fishing, for which the ability to see beneath the surface of the water is crucial.
A mirrored coating can also be applied to the lens. This mirrored coating deflects some of the light when it hits the lens so that it is not transmitted through the lens, making it useful in bright conditions; however, it does not necessarily reflect UV radiation as well. Mirrored coatings can be made any color by the manufacturer for styling and fashion purposes. The color of the mirrored surface is irrelevant to the color of the lens. For example, a gray lens can have a blue mirror coating, and a brown lens can have a silver coating. Sunglasses of this type are sometimes called mirrorshades. A mirror coating does not get hot in sunlight and it prevents scattering of rays in the lens bulk.
Sunglass lenses are made of either glass or plastics. Plastic lenses are typically made from acrylic,polycarbonate ,CR-39 or polyurethane. Glass lenses have the best optical clarity and scratch resistance, but are heavier than plastic lenses. They can also shatter or break on impact. Plastic lenses are lighter but are more prone to scratching. Plastic offers more resistance to shattering than glass. Polycarbonate plastic lenses are the lightest, and are also almost shatterproof, making them good for impact protection. CR-39 is the most common plastic lens, due to low weight, high scratch resistance, and low transparency for ultraviolet and infrared radiation.
Any of the above features, color, polarization, gradation, mirroring, and materials, can be combined into the lens for a pair of sunglasses. Gradated glasses are darker at the top of the lens where the sky is viewed and transparent at the bottom. Corrective lenses or glasses can be manufactured with either tinting or darkened to serve as sunglasses. An alternative is to use the corrective glasses with a secondary lenses such as oversize sunglasses that fit over the regular glasses, clip-on lens that are placed in front of the glasses, and flip-up glasses which feature a dark lens that can be flipped up when not in use (see below). Photochromic lens gradually darken in bright light.
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