The refractive index of the lens is an important parameter of the lens, which is usually 1.49, 1.56, 1.61, 1.67 and other numbers. These figures represent the optical refractive index of the lens. That is, when the center thickness of the lens is the same, the lenses with the same degree of the same material have thinner edges than the low refractive index lenses. The bigger the number is, the thinner the lens is, the higher the price will be.

Currently on the market 1.49 lenses have been rare, but not many varieties, which are some of the elderly to buy reading glasses. And myopia within 500 degrees in the general choice of refractive index of 1.56 is the best, such lenses are complete, many functions, and the price is moderate. If people in more than 500 degrees of myopia because of the thickness, so when the choice in the purchase of lens refractive index in the refraction of 1.56 or 1.61 aspheric lenses are good rate.

From a large number of statistics we have found that most of the patients wear a middle degree lens. The use of traditional medium and low refraction lenses will often give people a "very thick" feeling, especially a high number of lenses. The 1.67 high refraction resin lenses are lighter and thinner than the ordinary resin lenses. As a result of：

1, the high refractive index with aspheric design, curved slim appearance, but also can effectively resist ultraviolet radiation and reduce the infrared, eliminate interference, computer TV radiation.

2. Because of its greater density, it is more wear-resistant and thinner, and is not easily scratched and lighter.

This article introduces several simple and easy methods based on the experience of the lens manufacturing and the international experience.

The physical properties of the resin lenses

2.1 refractive index: the ratio of the medium specific to the sine of the angle of transmission light from the incident light in the air and the angle of the incident light. Its value is slightly different because of the difference in the measurement of the baseline wavelength and the environment. For lenses with same refractive index and thickness, refractive index is inversely proportional to lens thickness and transmittance, and its value is generally between 1.49~1.74.

2.2 transmittance: the ratio of the transmittance of a medium to the amount of incident light, expressed as a percentage. For optical lenses, the higher the transmittance, the smaller the reflection and absorption, the clearer the lenses are. According to the principle of the half wave superposition of the wave theory, the transmittance of the lens can be improved by the combination of hard and multiple refractive index. Generally speaking, no transparent resin lens coated rate between 88%~93%. In some cases, the light transmittance may be reduced artificially because of the need for other special functions, but it must be met (see the national standard QB2457-1999).

When the sunglasses meet the requirements, reached the basic requirements for protection, which also blocked the corresponding amount of UV in blocking the light at the same time, wearing the sunglasses will not increase the amount of light received at least (wearing sunglasses will reduce people into the eye pupil wearing flux, resulting in increases in the same external conditions if you can not stop, UV Sunglasses a corresponding amount of human will receive more light than wearing sunglasses when). In November 2006, the official implementation of the national standard GB10810.3 (ophthalmic lenses and related products: the third part: transmittance standard and measurement method) clearly stipulates that the highest transmittance of sunglasses should not exceed 5%.

2.3 Abbe number: the countdown lens dispersion coefficient, interference resolution and color characterization of lenses for visible light, refractometer measured available accuracy of not less than 3 x 10 - 4. Its value is between 32~60 and the higher the Abbe number of the lens, the less distortion to the incident visible light.

China's anti scratch performance of resin lenses has clear mandatory provisions, and methods for detecting the quantitative explain (see "GB QB2506-2001 optical resin glasses with universal detection method"), according to the test requirements, we can be tested by the physical device is simple, the use of ATAGO (aituo) resin refractive index Abbe refractometer, Tester (NAR-4T, solid-liquid) high refractive index NAR-1T Abbe refractometer detection SOLID, lens transmittance, refractive lens (digital) Abbe refractometer with DR-A1 (Abbe number) multi wavelength series refractometer DR-M2 can be directly measured (Abbe number) instrument in refractive lens the rate in the process of providing application solutions.