Polycarbonate lenses are not only thinner and lighter in weight than traditional plastic eyeglass lenses, they offer (UV) protection and scratch resistance. They are very impact resistant extra strong ideal for children’s glasses, sports eyewear, safety glasses, rimless frames.
Thin lenses hight index
High-index lenses (left) can be considerably thinner and lighter, even in a strong prescription. Lenses made of high-index plastic are lighter than the same lenses made in conventional plastic, and more comfortable to wear. High-index glass lenses also have thinner edges, but high-index glass is heavier than conventional glass, so there is not as much weight savings with glass as there is with plastic lenses.The overwhelming popularity of the first high-index lenses has led to the development of a variety of high-index materials, which are classified by how they bend light. This is a ratio that compares the speed of light traveling through a clear material with the speed of light traveling through air. For conventional plastic lenses, the index is 1.50. For glass, it is 1.52. Any lense material with an index higher than that of glass or plastic is considered to be high index. High-index plastic lenses are now available in a wide variety ranging from 1.53 to 1.71. Most of today’s fashionable frames are made of plastic or metal with rims thinner than the lens itself. Also very popular are rimless mountings, where the lens edges are completely exposed. In either case, the lense edges are highly visible, and thicker edges can detract from the appearance of the eyewear.
Thin Aspheric Lenses
In 1990 a new type of lense called “aspheric” come out. This type of lenses was rapidly became one of the most popular lenses categories. Aspheric lenses have a more complex front surface that gradually changes curve from the center of the lense all the way out to the edge. Both myopes and hyperopes can benefit from aspheric lenses, because they are thinner than regular lenses and provide better vision. In minus (nearsighted) lenses, the surface gradually steepens toward the lens edge. This gradually changing surface provides a number of important benefits, most important of which is that vision through an aspheric lens is usually superior to vision through a conventional lens. In an aspheric design, the lenses have flatter curves; this means lenses do not “bulge” out of the frame as much as regular lenses. The side profile of aspheric lenses is thinner, which greatly enhances the appearance of finished eyewear.
Photochromic and Color Lenses
Photochromic lenses change from light to dark depending on the amount of ultraviolet light they are exposed to. The lenses are available in either gray or brown colors that are light enough to wear indoors and darken to sunglass shade when exposed to ultraviolet light, Performance features include advanced variable-tint technology that allows rapid darkening when you go outside (and rapid return to clear when you go in), with 100% UV protection. They have a front-surface coating that changes color (to gray or brown tint) when exposed to ultraviolet light. The changeable coating means that the color darkens evenly regardless of lens prescription or thickness. Sun-sensitive lenses are also called “photochromic” and “transition”. They are available in glass, hard resin and polycarbonate. Originally made to darken to a moderate shade, new versions are available that darken to a true sunglass. Because photochromic lenses react to UV light and not to visible light, there are circumstances under which the darkening will not occur. A perfect example of this is when you’re in your car. Because the windshield blocks out most of the UV light, photochromic lenses will not darken inside the car. For this reason, most sunglasses with photochromic lenses also have a certain amount of tint already applied to them.
These are the exciting sunglasses that eliminate reflected glare. They are especially appropriate for drivers, fisherman, hunters and all types of outdoors activities. Light reflected from surfaces like a flat road or smooth water is generally horizontally polarized. This horizontally polarized light is blocked by the vertically oriented polarizers in the lenses. The result: a reduction in annoying and sometimes dangerous glare. The bottom line is that whether you spend your time boating or waterskiing, in-line skating or mountain biking, driving at night or jogging at noon, polarized sunglasses are an excellent choice for sun wear, These sunglasses can be used for driving and in fact can reduce the glare that comes off a long, flat surface such as the hood of the car or the surface of a road, a reduction in annoying and sometimes dangerous glare
Because of the presence of the two allyl functional groups, the monomer can not only polymerize but also cross-link which results in a thermoset plastic characterized by being hard, infusible and insoluble in all solvents. In addition, CR39 homopolymer is a high-grade optical plastic whose index of refraction is just slightly less. CR39 lenses are colorless and completely transparent to the visible light and almost completely opaque in infrared and ultraviolet region of the spectrum, as a result are far more comfortable to wear. CR39 lenses are shatterproof and hence a must for children where, even in case of an impact it does not splinter into pieces.
Bifocals (meaning their two points of focus, mainly one for distance and one for near) are some of the most commonly prescribed multifocal lenses. A small portion of the bifocal eyeglass lenses is reserved for the near-vision correction. The rest of the lense is usually a distance correction, but sometimes has no correction at all in it, if you have good distance vision. The segment that is devoted to near-vision correction can be in one of several shapes, Generally, you look up and through the distance portion of the lense when focusing on points farther away and look down and through the bifocal segment of the lense when focusing on reading material or detail work up to about 18 inches away.
Progressive lenses, sometimes referred to as no-line bifocals, not only provide visual correction for distances that traditional bifocals can’t, but they also hide the fact that you even need reading glasses. Progressive lenses are the closest to how natural vision is that you can get in a pair of prescription eyeglasses. They are more than just a defined near and distance correction in one lens. Progressive designs are available in regular plastic and glass, polycarbonate, high-index and photochromic lenses.
Multifocals let you focus through different prescriptions at different distances through the same lense. Bifocals (meaning a lense with two points of focus usually one for distance and one for near) are the most commonly prescribed multifocal lenses. Many people need some visual correction in order to read or see things close-up. multifocals are suited for performing a particular job or hobby and are not meant for everyday wear, Specialty multifocal lenses are designed to solve particular vision problems. Multifocal lenses whose corrective powers change progressively throughout the lense. A wearer looks through one portion of the lense for distance vision, another for intermediate vision, and a third portion for reading or close work. Each area is blended invisibly into the next, without the lines that traditional bifocals or trifocals have.