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Glasses – also called eyeglasses (formal), spectacles, or specs (informal) – are frames bearing lenses worn in front of the eyes, nirmally for vision correction or eye protection. Safety glasses are a kind of eye protection against flying debris or against visible and near visible ang near visible light or radiation. Sunglasses allow better vision in bright daylight, and may protect against damage from high levels of ultraviolet light. Other types of glasses may be used for vieweing visual information (such as stereoscopy) or simply just for aesthetic or fashion values.
Historical types of glasses include the pince-nez, monocle, lorgnette, and scissors or scissors-glasses.
Modern Glasses are typically supported by pads on the bridge of the nose and by template arms (sides) placed over the cars. CR-39 lenses are the most common plastic lenses due to their low weight, high scratch resistance, low dispersion, and low transparency to ultraviolet and infrared radiation. Polycarbonate and Trivex lenses are the lightest and most shatter-resistant, making the best for impact protection
An unpopular aspect of glasses is their inconvenience. Even through the creaton of light frames such as those made of titanium, very flexible frames, and new lens materials and optical coatings, glasses can still cause problems during rigorous sports. Visibility can be significantly educed by becoming greasy, trapping vapour when eating hot food, swimming, walking in rain or rapid temperature changes (such as walking int a warm building from cold temperature outside). Scraping fracturing or breakage of the lenses require tme-consuming and costly professional repair, though modern plastic lenses are almost indestructible and very scratch-resistant.
What is one good point of CR-39 lenses?
It is cheap.
It is the lightest.
It is not easily scratched.
Infrared can not get through it.
Ultraviolet can not get through it.
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M. Ardini
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