Sunglasses Common Knowledge
Sunglasses are a kind of protective glasses. The invention of sunglasses has a history of two thousand years. The ancient Romans used colored glass pieces to shield their eyes to reduce sunlight stimulation, which was the earliest prototype of sunglasses. With the continuous progress of social civilization, the fashion attribute of sunglasses has been attached more and more importance by most people. In the eyes of many young people, sunglasses represent the language of summer and the scenery of the scorching sun. In fact, the fundamental purpose of sunglasses is to provide radiation protection for the eyes.
There are many kinds of light in nature that can cause damage to human eyes, mainly ultraviolet light, strong visible light and infrared light. Which UV is the most harmful to the human eye, long-term absorption of UV on the eye cornea, crystal, retina, etc., will have a destructive effect, will lead to photochemical keratopathy, cataracts, retinopathy and other eye diseases. Therefore, it is necessary to wear a pair of sunglasses to provide radiation protection for the eyes of people who often work or live in a bright light environment. Menghai Shi, Optometry and Refractive Surgery Center, Henan Provincial Eye Hospital
Sunglasses mainly through filtering the harmful light to achieve the purpose of protection, according to its principle can be divided into absorption, reflection, polarization and interference. Absorption filters are usually made by adding metal oxides to the lenses, such as iron oxide, cobalt oxide, and chromium oxide, which absorb ultraviolet and infrared rays. Reflective filter is by plating a layer of metal film on the surface of the lens, which mainly reflects the infrared ray and has poor protection against ultraviolet rays. The polarization filter can remove 98% random reflected light and 96% ultraviolet light through the polarization layer. Interference filters filter radiation by changing the wavelength of light through multiple layers of electrical insulating film. In addition, sunglasses can be classified in other ways as follows, according to the color of the lens: gray, tawny, green, blue, mercury, yellow, etc. Frame material: metal, plate; According to the lens: dyeing type, discoloration type, clip type, set mirror type; According to the lens design: monochrome, gradient color.
The first thing to consider when choosing sunglasses is protection. The UV index is a very important objective indicator. The UV index is the rate of UV filtering. Most sunglasses have a UV index between 96% and 98%, and dark lenses are better than light ones. Consumers can understand by viewing the UV label on the lens, according to the F?D?A standard, the lens in the guarantee of transmittance at the same time, to filter more than 90% of the sunlight in the UV, the lens should be labeled "UV-100protct10n" label, when 100% filter UV, should be labeled "UV-400protct10n" label.
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