![]() ![]() So, the higher the refractive index of a lens material, the less lens material is required to bend light to the same degree as a lens with a lower refractive index. The higher the refractive index of a material, the slower light moves through it, which results in greater bending (or focusing) of the light rays. This means light travels roughly 50% slower through CR-39 plastic than it does through a vacuum. For example, the index of refraction of CR-39 plastic is 1.498. Specifically, the refractive index of a lens material is the ratio of the speed of light in a vacuum, divided by the speed of light in the lens material. ![]() This efficiency is related to how fast light travels through the material. ![]() The index of refraction (or refractive index) of an eyeglass lens material is an indicator of how efficiently the material refracts (bends) light. Here are details about important features of lenses for your glasses: Index of refraction Significantly more impact-resistant than CR-39 plastic and high-index plastic lenses (except polycarbonateÄownside: Not yet available in a wide variety of lens designs. ![]() Less costly than 1.70-1.74 high-index lenses. Except for the crown glass, these are all plastic materials. Here are popular eyeglass lens materials, arranged in order of refractive index and lens thickness (pretty good indicators of cost). They have a higher index of refraction and are available in an aspheric lens design (see below for more about these). These lenses are significantly thinner and lighter than regular plastic lenses. In the past 20 years, several different types high-index plastic lenses have been introduced. They are lightweight and have slightly different optical and impact resistance qualities. Trivex lenses are a good alternative to polycarbonate lenses. Trivex, a new lightweight and impact-resistant eyeglass lens material, was introduced in 2001. Polycarbonate is a great lens material for children's eyeglasses, safety glasses and sports eyewear. They are lighter than regular plastic eyeglass lenses and significantly more impact resistant. Since then, polycarbonate lenses have surged in popularity. The first lightweight polycarbonate lenses for safety glasses were introduced in the 1970s. They also are more impact-resistant than glass lenses. They are relatively inexpensive and have excellent optical qualities. Plastic eyeglass lenses are about half the weight of glass lenses. These lightweight alternatives to glass lenses were call CR-39 plastic lenses. The first plastic eyeglass lenses were developed in the 1940s. For these reasons, glass lenses are no longer widely used for eyeglasses. But hey are heavy and can break easily, potentially causing a serious eye injury or even loss of an eye. In the early days of vision correction, all eyeglass lenses were made of glass. It will also help you choose the best progressive lenses or other multifocal lenses if you have presbyopia. It applies to prescription eyeglass lenses that correct nearsightedness, farsightedness and astigmatism. The following information will help you buy eyeglasses lenses wisely. The lenses you choose for your glasses influence four factors: There are many different types of eyeglsass lens materials and designs, and each has its own features, benefits, and cost. And buying the best lenses for your glasses is not an easy task. The type of lenses in your glasses play a big role in your vision, comfort and safety when wearing eyeglasses. By Gary Heiting, OD Glasses lenses: Overview ![]()
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