Yishikang popular science lecture series-glasses related knowledge At present, there are many kinds and brands of glasses. In order to describe the problem conveniently, we usually discuss it according to the materials and specifications of lenses. First, according to the material classification. Glass can be divided into three categories by material: spar, glass and plastic. 1. Flake crystal is a kind of natural timely crystal, and its main component is silica. According to experts, spar belongs to low-grade gemstones. From the perspective of gemstones, spar can be divided into five categories: price-to-book ratio, price-to-book ratio, small cotton, medium cotton and large cotton ("cotton" refers to the asbestos effect in spar). The best cotton in the city is the worst. At present, there are two kinds of crystal chips on the market: natural crystal chips and artificial crystal chips. Among them, artificial spar can be divided into melting spar and generating spar according to different manufacturing methods. Crystal has a large specific gravity and high hardness, and is not easy to process. It can't block and absorb infrared rays and ultraviolet rays like a glass sheet. Rock crystal often has birefringence, uneven material and high price. Therefore, as glass, crystal sheet has been gradually replaced by glass sheet and plastic sheet. 2. Glass flake glass is mainly composed of various oxides such as silicon dioxide, which can be divided into ordinary glass and optical glass. Next, we will discuss the spectacle lens of optical glass. Optical glass sheets can be divided into colorless and colored ones. Among them, colorless optical glass sheets are divided into light white sheets and high refractive index sheets; Colored optical glass sheets are divided into colored glass sheets, optical X-rays, optical X-rays and color-changing sheets. (1) pale white lenses are usually used to make flat, nearsighted, hyperopia, astigmatism and bifocal (including multifocal) lenses. If the oxides of titanium and cerium are added to the white sheet material, the lens can absorb ultraviolet rays with a wavelength below 330nm, and this lens becomes an ultraviolet white sheet again. This kind of lens is suitable for field workers, drivers and microcomputer operators. (2) High refractive index sheet, also called "ultra-thin sheet", is a kind of flint glass containing lead oxide. Because of its high refractive index, under the same diopter, the lens curvature is shallower, the lens thickness is thinner, and the lens is light and beautiful, which is suitable for the manufacturing and processing of high-altitude lenses. (3) Colored glass sheets Various colorants are added to colorless optical glass sheets to make the glass appear gray, green, blue, red, yellow and other colors. Colored glass sheets are mainly used to protect eyes and glasses from harmful rays. (4) Optical X-ray, which is called optical X-ray for short, is based on barium crown glass and added with oxides such as cerium, titanium and praseodymium, which can absorb ultraviolet rays with wavelengths below 340nm. The light gram is light purple under incandescent lamp and light blue under sunlight, which is called bicolor effect. Guangke film is light blue in the sun, so it is also called X-ray film. Guangke is generally used to process plain lenses, low-beam and hyperopia lenses, three-beam lenses and double-beam lenses (including multi-beam lenses), and dark grams can also be used as sunglasses lenses. Especially suitable for field workers, drivers, microcomputer operators and so on. (5) Optical plug, referred to as optical plug, is made by adding oxides such as manganese and cerium on the basis of barium crown glass, and can absorb ultraviolet rays with wavelength below 350nm. The light distribution film is light pink, so it is also called Cosay red film. The application scope of optical matching film is the same as that of optical gram film. (6) The color-changing sheet is called photochromic glass sheet, which is made by adding silver halide and other substances into colorless or colored glass materials. When the lens is irradiated by light, silver halide is decomposed into silver and halogen, and the color of the lens changes from bright to dark. When the light darkens, silver and halogen combine and the lens returns to its original colorless or primary color state. There are two commonly used color-changing films: tea change and gray change. If neodymium, praseodymium and other elements are added, the lens will also change in blue, gray, pink and brown. Color-changing films are generally used to process plain lenses, myopia lenses and hyperopia lenses, and in recent years, they are also used to process bifocal lenses. The color-changing film is characterized by correcting vision and making sunglasses. 3. Plastic sheet plastic, also known as optical plastics or optical resin, is a polymer organic compound, which is molded by die casting or injection molding. Plastic materials can be divided into thermosetting and thermoplastic. The biggest advantage of plastic sheet is that the lens is not fragile, even if it is broken, it is not as sharp as glass sheet, so it is especially suitable for children, students, sports workers, field workers and drivers. In this regard, some countries specifically stipulate that the above-mentioned personnel must prepare plastic lenses. In this sense, the market share of plastic lenses will increase year by year and eventually replace glass sheets. There are three kinds of plastic sheets: acrylic, Cr-39 and PC, which we will explain in detail later. Second, according to the specifications and uses of lenses. 1. Lens specifications are divided into diameter specifications and thickness specifications. The lens diameter specification is usually given by the lens manufacturer. In recent years, the specifications of lens diameter tend to be larger, such as 60mm, 65mm or even 70mm, to meet the requirements of lens displacement. Small-diameter lenses are rarely seen now. The lens thickness specification is also given by the lens manufacturer. According to the degree of the lens, the blank lens with corresponding thickness can be selected. The thinnest part of the processed glass lens should not be less than 0.7mm, and the thickness of plastic lens depends on different materials. Please refer to the national standard GB10810-1999 glasses and the standard QB2506-200 1+0 optical resin glasses of the Ministry of Light Industry, so I won't go into details next time. 2. The purpose of the lens According to the purpose, the lens is divided into spherical lens, astigmatism lens (cylindrical lens), prism lens and special lens. Among them, spherical lenses are divided into plain lenses, myopia lenses and hyperopia lenses; Special lenses are divided into bifocal lenses, multifocal lenses, progressive multifocal lenses, coated lenses, polarizing lenses, optometric lenses and contact lenses. This information comes from Beijing list network. More information about other trainings in Beijing can be found in the list.