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A photochromic eyeglass lens, part of the lens darkened after exposure to sunlight while the other part remained covered. 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.
A photochromic eyeglass lens, after exposure to sunlight while part of the lens remained covered by paper. Photochromism is the reversible change of color upon exposure to light. It is a transformation of a chemical species ( photoswitch ) between two forms by the absorption of electromagnetic radiation ( photoisomerization ), where the two ...
Transitions Optical is a U.S.-based company known for manufacturing photochromic lenses, which darken on exposure to specific types of light. The company was founded in 1990. [1] In 1991, Transitions Optical became the first company to commercialize and manufacture plastic photochromic lenses. [2]
Electronic: Transitions in electron energy levels within the atom (e.g., pigments). These transitions are typically in the ultraviolet (UV) and/or visible portions of the spectrum. Vibrational: Resonance in atomic/molecular vibrational modes. These transitions are typically in the infrared portion of the spectrum.
Variable tint or photochromic lenses increase their optical density when exposed to UV light, reverting to their clear state when the UV brightness decreases. Car windscreens filter out UV light, [ 53 ] [ 54 ] slowing and limiting the reaction of the lenses and making them unsuitable for driving as they could become too dark or too light for ...
improved lens manufacturing and measurement technology. Today the complex surfaces of a progressive lens can be cut and polished on computer-controlled machines, allowing 'freeform surfacing', as opposed to the earlier casting process, thus explaining the difference in price.
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