Glasses - also called eyeglasses (formal), spectacles, or specs (informal) - are frames bearing lenses worn in front of the eyes, normally for vision correction or eye protection. Safety glasses are a kind of eye protection against flying debris or against visible and 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 viewing visual information (such as stereoscopy) or simply just for aesthetic or fashion values. Historical types of glasses include the prince-nez, monocle, lorgnette, and scissor or scissors-glasses. Modern glasses are typically supported by pads on the bridge of the nose and by temple arms (sides) placed over the ears. CR-39 lenses are the most common plastics 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 them the best for impact protection. An unpopular aspect of glasses is their inconvenience. Even through the creation 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 reduced by becoming greasy, trapping vapour when eating hot food, swimming, walking in rain or rapid temperature changes ( such as walking into a warm building from cold temperature outside). Scraping, fracturing, or breakage of the lenses require time-consuming and costly professional repair, though modern plastics lenses are almost indestructible and very scratch-resistant. What is one good point of CR-39 lenses?

Question

Glasses - also called eyeglasses (formal), spectacles, or specs (informal) - are frames bearing lenses worn in front of the eyes, normally for vision correction or eye protection. Safety glasses are a kind of eye protection against flying debris or against visible and 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 viewing visual information (such as stereoscopy) or simply just for aesthetic or fashion values.

Historical types of glasses include the prince-nez, monocle, lorgnette, and scissor or scissors-glasses.

Modern glasses are typically supported by pads on the bridge of the nose and by temple arms (sides) placed over the ears. CR-39 lenses are the most common plastics 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 them the best for impact protection.

An unpopular aspect of glasses is their inconvenience. Even through the creation 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 reduced by becoming greasy, trapping vapour when eating hot food, swimming, walking in rain or rapid temperature changes ( such as walking into a warm building from cold temperature outside). Scraping, fracturing, or breakage of the lenses require time-consuming and costly professional repair, though modern plastics lenses are almost indestructible and very scratch-resistant.

What is one good point of CR-39 lenses?

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