subject: Spectacles Are Usually Called Glasses Or Eyeglasses. [print this page] Glasses are worn in front of the eyes for vision alteration, or eye protection. Sometimes glasses are used to guard the eyes from UV rays.
The current day glasses are supported with pads on the bridge of the nose. Usually the temple arms are sited over the ears.
Eyeglass lenses are mostly made of plastic. But occasionally they are made of glass too. The plastic which lenses contain CR- 39 and polycarbonate. These materials are quite suitable for sunglass lenses since these reduce the danger of breakage and weigh less than glass lenses. Read more Pladearbejde
Some plastics have more helpful optical properties than glass, such as better transmission of visible light and better absorption of ultra violet light. Also some plastics have a greater index of diversion than most types of glass, which is useful in the making of corrective lenses shaped to correct many vision abnormalities such as myopia, allowing thinner lenses for a given prescription.
Sunglasses were used in China in the 12th century, but they did not offer any corrective pay backs. These glasses were in the form of flat panes of smoky quartz and they protected the eyes from shine.
Bifocals were created by the American scientist Benjamin Franklin in 1784. He suffered from both myopia and presbyopia and hence had to regularly switch between two pairs of glasses. This interested him to invent the bifocals.
Scratch resistant coatings can be applied to most plastic lenses giving them like scratch resistance to glass. Read more Vinduespudsning Sjaelland
All glasses are not designed for eye correction alone. Selected glasses are worn for fashion or aesthetic value.
Safety glasses are a kind of eye protection against flying debris or against visible or near visible light or radiation.
The power of a lens is usually measured in diopters. Glasses amending for myopia or nearsightedness will have harmful diopter strengths and glasses correcting for hypermetropia will have helpful diopter strengths.
Nylon frames are usually used for guard eyewear for sports because of their light weight and supple properties.
Polycarbonate is usually used to manufacture safety lenses. This is basically jet windshield plastic and very doubtful to break.
Modern safety glasses tend to be given a more stylish design in order to encourage their use. Read more Gravearbejde Sjaelland
There are safety glasses for welding too. These glasses are used when a complete sized welding helmet is inconvenient. These welding glasses are called flash goggles, because they provide protection from welding flash.
