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Photochromic Lens
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. They are principally used in glasses that are dark in bright sunlight, but clear, or more rarely, lightly tinted in low ambient light conditions. They darken significantly within about a minute of exposure to bright light and take somewhat longer to clear. A range of clear and dark transmittances is available. In one sort of technology, molecules of silver chloride or another silver halide are embedded in photochromic lenses. They are transparent to visible light without significant ultraviolet component, which is normal for artificial lighting. In another sort of technology, organic photochromic molecules, when exposed to ultraviolet (UV) rays as in d ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Optical Lens
A lens is a transmissive optical device which focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements''), usually arranged along a common axis. Lenses are made from materials such as glass or plastic, and are ground and polished or molded to a desired shape. A lens can focus light to form an image, unlike a prism, which refracts light without focusing. Devices that similarly focus or disperse waves and radiation other than visible light are also called lenses, such as microwave lenses, electron lenses, acoustic lenses, or explosive lenses. Lenses are used in various imaging devices like telescopes, binoculars and cameras. They are also used as visual aids in glasses to correct defects of vision such as myopia and hypermetropia. History The word '' lens'' comes from '' lēns'', the Latin name of the lentil (a seed of a lentil p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
University College London
, mottoeng = Let all come who by merit deserve the most reward , established = , type = Public research university , endowment = £143 million (2020) , budget = £1.544 billion (2019/20) , chancellor = Anne, Princess Royal(as Chancellor of the University of London) , provost = Michael Spence , head_label = Chair of the council , head = Victor L. L. Chu , free_label = Visitor , free = Sir Geoffrey Vos , academic_staff = 9,100 (2020/21) , administrative_staff = 5,855 (2020/21) , students = () , undergrad = () , postgrad = () , coordinates = , campus = Urban , city = London, England , affiliations = , colours = Purple and blue celeste , nickname ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Glass Compositions
Glass is a non-crystalline, often transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling (quenching) of the molten form; some glasses such as volcanic glass are naturally occurring. The most familiar, and historically the oldest, types of manufactured glass are "silicate glasses" based on the chemical compound silica (silicon dioxide, or quartz), the primary constituent of sand. Soda–lime glass, containing around 70% silica, accounts for around 90% of manufactured glass. The term ''glass'', in popular usage, is often used to refer only to this type of material, although silica-free glasses often have desirable properties for applications in modern communications technology. Some objects, such as drinking glasses and eyeglasses, are so commonly made of silicate-based glass that they are simply called by the name of the material. Despite be ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chromism
In chemistry, chromism is a process that induces a change, often reversible, in the colors of compounds. In most cases, chromism is based on a change in the electron states of molecules, especially the π- or d-electron state, so this phenomenon is induced by various external stimuli which can alter the electron density of substances. It is known that there are many natural compounds that have chromism, and many artificial compounds with specific chromism have been synthesized to date. It is usually synonymous with chromotropism, the (reversible) change in color of a substance due to the physical and chemical properties of its ambient surrounding medium, such as temperature and pressure, light, solvent, and presence of ions and electrons. Chromism is classified by what kind of stimuli are used. Examples of the major kinds of chromism are as follows. * thermochromism is chromism that is induced by heat, that is, a change of temperature. This is the most common chromism of all. * p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Corrective Lenses
A corrective lens is a lens (i.e. a transmissive optical device) that is typically worn in front of the eye to improve daily vision. The most common use is to treat refractive errors: myopia, hypermetropia, astigmatism, and presbyopia. Glasses or "spectacles" are worn on the face a short distance in front of the eye. Contact lenses are worn directly on the surface of the eye. Intraocular lenses are surgically implanted most commonly after cataract removal but can be used for purely refractive purposes. Prescription of corrective lenses Corrective lenses are typically prescribed by an ophthalmologist or an optometrist. The prescription consists of all the specifications necessary to make the lens. Prescriptions typically include the power specifications of each lens (for each eye). Strengths are generally prescribed in quarter- diopter steps (0.25 D) because most people cannot generally distinguish between smaller increments (e.g., eighth-diopter steps / 0.125 D). The u ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Essilor
Essilor International is a French-based international ophthalmic optics company that designs, manufactures and markets lenses to correct or protect eyesight. Its headquarters is in Charenton-le-Pont (near Paris), France. It is the world's largest manufacturer of ophthalmic lenses. The firm is responsible for creating Varilux, the world's first progressive lens, which corrects presbyopia and allows clear vision in the wearer's near, intermediate and far vision. The company formed from the merger of ophthalmic firms ''Essel'' and ''Silor'' in 1972. In January 2017 Essilor announced a merger with Italian eyewear giant Luxottica. On 1 October 2018, the new holding company EssilorLuxottica was born, resulting in combined market capitalization of approximately €57 billion. History 1849–1972: Essel and Silor ''Essel'' (Société des Lunetteries) was founded in 1849 (then-called ''L'Association Fraternelle des Ouvriers Lunetteries'') as a small network of eyeglass assembly ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Photosensitive Glass
Photosensitive glass, also known as photostructurable glass (PSG) or photomachinable glass, is a crystal-clear glass that belongs to the lithium-silicate family of glasses, in which an image of a mask can be captured by microscopic metallic particles in the glass when it is exposed to short wave radiations such as ultraviolet light. Photosensitive glass was first discovered by S. Donald Stookey in 1937.Paul, p. 333Encyclopædia Britannica, pp. 194–209Maluf, pp. 62–63 History Photosensitive glass was invented in November 1937 by Dr. Donald Stookey of the Corning Glass Works. It was announced publicly ten years later on June 1, 1947. It was patented in 1950 by Stookey as U.S. Pat. No. 2,515,937 and U.S. Pat. Nos. 2,515,943 with gold microscopic particles and marketed under the trade name PhotoCor. Exposure process When the glass is exposed to UV light in the wavelength range 280–320 nm, a latent image is formed. The glass remains transparent at this stage, but its a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Persol
Persol is an Italian eyewear brand specializing in the manufacturing of sunglasses and optical frames. It is one of the oldest eyewear companies in the world and is owned by the Luxottica group. The name is derived from the Italian ''per il sole'', meaning "for the sun". Formed in 1917 by Giuseppe Ratti, Persol originally catered to pilots and sports drivers. Presently, the company markets durable sports sunglasses. The company trademark is a silver arrow. History In 1917 Giuseppe Ratti, owner of Berry optical, started producing his first glasses and lenses for athletes and aviators. The company developed a flexible stem, known as the patented Meflecto system, which was one of the first spring hinges for eyewear. Persol was introduced to the United States in 1962 and opened its first boutique on Rodeo Drive in Beverly Hills in 1991. Technology Currently all plastic Persol spectacles are made in Italy using cellulose acetate In biochemistry, cellulose acetate refers to an ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Serengeti (sunglasses Brand)
Serengeti Eyewear is a sunglasses line owned by Bollé Brands. Their main focus is eye protection, of which the company researches and develops technology such as photochromic lenses, polarized lenses, spectral control, among others. History The brand was developed by Corning. In 1984, Corning considered closing Serengeti due to poor financial performance. However, entrepreneur Zaki Mustafa convinced the board that he could save the brand. He attributed poor sales to a product-centric focus, poor marketing, anemic customer service, and inefficient asset management. With only fifty-two employees, he successfully raised sales from $5 million in 1985 to $62 million in 1992. The Serengeti brand was acquired by Bushnell in September 2000. Bollé, Cébé and Serengeti were part of Vista Outdoor's acquisition of Bushnell in 2013. In July 2018, Vista Outdoors announced it had reached an agreement with a European private equity fund to sell the Bollé, Cébé and Serengeti eyewe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sunglass
Sunglasses or sun glasses (informally called shades or sunnies; more names below) are a form of protective eyewear designed primarily to prevent bright sunlight and high-energy visible light from damaging or discomforting the eyes. They can sometimes also function as a visual aid, as variously termed spectacles or glasses exist, featuring lenses that are colored, polarized or darkened. In the early 20th century, they were also known as sun cheaters (cheaters then being an American slang term for glasses). Since the 1930s, sunglasses have been a popular fashion accessory, especially on the beach. The American Optometric Association recommends wearing sunglasses that block ultraviolet radiation (UV) whenever a person is in the sunlight to protect the eyes from UV and blue light, which can cause several serious eye problems. Their usage is mandatory immediately after some surgical procedures, such as LASIK, and recommended for a certain time period in dusty areas, when leav ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cation
An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convention. The net charge of an ion is not zero because its total number of electrons is unequal to its total number of protons. A cation is a positively charged ion with fewer electrons than protons while an anion is a negatively charged ion with more electrons than protons. Opposite electric charges are pulled towards one another by electrostatic force, so cations and anions attract each other and readily form ionic compounds. Ions consisting of only a single atom are termed atomic or monatomic ions, while two or more atoms form molecular ions or polyatomic ions. In the case of physical ionization in a fluid (gas or liquid), "ion pairs" are created by spontaneous molecule collisions, where each generated pair consists of a free electron an ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
