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A photochromic lens is an optical lens that darkens on exposure to light of sufficiently high frequency, most commonly ultraviolet (UV) radiation. In the absence of activating light, the lenses return to their clear state. Photochromic lenses may be made of polycarbonate, or another plastic. Glass lenses use visible light to darken.
Medical experts advise the public on the importance of wearing sunglasses to protect the eyes from UV; [26] for adequate protection, experts recommend sunglasses that reflect or filter out 99% or more of UVA and UVB light, with wavelengths up to 400 nm. Sunglasses that meet this requirement are often labeled as "UV400".
Typical sunglasses lenses are tinted for protection against bright light or polarized to remove glare; photochromic glasses are clear or lightly tinted in dark or indoor conditions, but turn into sunglasses when they come into contact with ultraviolet light. Most over-the-counter sunglasses do not have corrective power in the lenses; however ...
[49] [48] Sunglasses make up 42% of the global eyewear market as of 2020. They protect the eyes from sun damage and conjunctivitis, but are also sold as fashion accessories, with many consumers opting to have a number of sunglasses for different occasions. [48] EssilorLuxottica controls a dominant portion of the eyewear retail market.
Safety glasses or spectacles, although often used as a catch-all term for all types of eye protection, specifically revers to protective equipment that closely resembles common eye wear. To meet most national standards, spectacles must include side shields to reduce the ability of debris to get behind the lenses from the side.
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