Why is Choosing the Right Spectacle Lens so Important?

As a Dome lens Manufacturer, share with you. When buying glasses, the choice of frames is crucial to the appearance and comfort of wearing glasses. But the glasses lens you choose will affect four factors: appearance, comfort, vision and safety.

A common mistake that people often make when buying glasses is not spending enough time to consider their choice of lens materials, designs and coatings.

This article provides you with the basic knowledge you need to buy eyeglass lenses wisely.

Optical Glass Lense

The following information applies to all spectacles-whether you need monocular lenses to correct nearsightedness, hyperopia and/or astigmatism, or progressive lenses, bifocals or other multifocal lenses to correct presbyopia.

Spectacle lens material-functions and advantages

Glass lenses. In the early stages of vision correction, all spectacle lenses were made of glass.

Although glass lenses provide excellent optical performance, they are heavy and can easily break, potentially causing serious damage to the eyes and even blindness. For these reasons, glass lenses are no longer widely used in glasses.

Polycarbonate lens. Polycarbonate was originally developed for Air Force helmet masks, used as "bullet-proof glass" for banking and other security applications. It is lighter and more impact resistant than CR-39 plastic, making it suitable for children’s glasses, safety glasses and sportswear The preferred material for glasses.

High refractive index plastic lens. In the past 20 years, in response to the demand for thinner and lighter glasses, many lens manufacturers have introduced high refractive index plastic lenses. These lenses are thinner and lighter than CR-39 plastic lenses because they have a higher refractive index and may have a lower specific gravity.

Refractive index

The refractive index of a spectacle lens material is a number, which is a relative measure of the efficiency of the material to refract light, and it depends on the speed of light propagation in the material.

Specifically, the refractive index of the lens material is the ratio of the speed of light in vacuum divided by the speed of light in the lens material.

For example, the refractive index of CR-39 plastic is 1.498, which means that the speed of light passing through CR-39 plastic is about 50% slower than the speed of passing through a vacuum.

The higher the refractive index of a material, the slower the light passing through it, resulting in greater bending (refraction) of light. Therefore, the higher the refractive index of the lens material, the less the lens material is required to bend light to the same extent as a lens with a lower refractive index.

In other words, for a given eye lens refractive power, a lens made of a material with a high refractive index will be thinner than a lens made of a material with a lower refractive index.

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