How do Plastic High Index Lenses Work?

The refractive index of the lens. The superscript 1.49, 1.56, 1.60, 1.67, 1.71, and 1.74 of the lens refer to the refractive index of the lens. For myopic glasses, under the same premise of other parameters, the higher the refractive index of the lens, the edge of the lens The lower the thickness ^[1] .

The refractive index of a lens is the ratio of the speed of light in a vacuum to the speed of light in a lens material, and reflects the ability of the lens to refract light.

At present, the refractive indices of the mainstream lenses on the market are: 1.56, 1.60, 1.67, 1.71, 1.74 and so on.

Under the same premise, the higher the refractive index of the lens, the thinner and lighter the lens. However, the higher the refractive index of the lens, the better. Generally, the higher the refractive index of the lens, the lower the Abbe number, and the more obvious the dispersion. With the upgrade of lens material technology, this law is gradually being broken. For example, the 1.71 refractive index lens has a refractive index higher than 1.56 and 1.67, but the Abbe number is higher than 1.67 refractive index lens and most of the 1.56 refractive index lens.

The common lenses in the market are roughly divided into glass, resin, PC and so on.

Among them, glass has a strong ability to refract light, so the refractive index of glass lenses can also be 1.80, 1.90. However, due to the fragility and heavy weight of glass lenses, glass lenses are generally selected only when ultra-high myopia requires 1.80, 1.90 refractive index lenses.

Due to its strong impact resistance, non-fragility, and good light refraction, resin lenses have attracted more and more attention, and now they have become the mainstream of the market.

With the development of the eyewear market, consumers' awareness of resin lenses has continued to increase, and at the same time, higher requirements have been placed on the performance and functions of products, which has led to a gradual decline in sales of low-refractive-index lenses, high-refractive-index lenses and excellent performance. Of lenses have attracted much attention from consumers.

In the past few years, few manufacturers independently developed and researched high-refractive-index lenses in the domestic market. High-refractive-index products are almost exclusively imported. Not only are they expensive, but their quality and performance cannot meet consumer requirements.

In recent years, some domestic manufacturers, self-built lens raw material factories, involved in the research and development of lens raw materials, independently developed a 1.71 high-refractive index lens series, including 1.71 daily general-purpose lenses, 1.71PMC super bright lenses, 1.71 blue light-resistant lenses, 1.71 Smart color-changing lenses, 1.71 multi-effect protective lenses, 1.71 progressive multi-focus lenses, to meet the diversified needs of consumers ^[2]

1. 1.71 Daily General Lens (Model: 71AS): Achieves high refractive index and low dispersion, making the glasses thinner, lighter and clearer.

2. 1.71PMC ultra-bright lens (model: 71KP): In order to further improve the clarity of the lens, the manufacturer re- purifies the lens raw materials, the raw materials are more pure, pure and translucent, the light transmittance is as high as 98.6%, waterproof and oil-proof, and anti-oxidation High performance, high-quality imaging brought by whitening and translucent.

3 , 1.71 intelligent color-changing lens (model: 71B): using the self-developed film-layer color-changing technology, the color-changing response is more rapid, darkening under outdoor UV irradiation, and turning back to transparent when indoor, the color of the lens can be adjusted automatically according to the strength of UV , One lens and two functions, automatically blocking ultraviolet rays, both fashionable and healthy.

4 , 1.71 anti-blue light lens (model: 71L): Modern people have been using computers and mobile phones for longer and longer, and the harmful blue light generated by electronic screens often causes irreversible damage to eyes. People with high myopia need to be more careful Take care of your eyes from harm, 1.71 anti-blue light series, using "film reflection + substrate absorption" innovative technology, to achieve dual dual-effect anti-blue light, filter harmful blue light, and retain beneficial blue light.

5 , 1.71 multi-effect protective lens (model: D71X): It has the dual effects of intelligent color changing and anti-blue light, effectively blocking outdoor strong light, blocking harmful blue light of electronic screens, and providing eye protection in a variety of scenarios, making vision healthy Protected at all times.

6 , 1.71 progressive multi-focus lens: to solve the user's vision needs for switching between near and far, a pair of glasses to meet the needs of wearing a variety of scenes, see far, middle and near vision are clear, easily respond to changing eye scenes. Students have three practical functions: reading and writing lenses, anti-fatigue lenses, and dimensional progressive lenses, which can meet the eye needs of users of different ages and easily adapt to the switching of far, middle and near vision.

The higher the refractive index of a material, the stronger the ability to refract incident light. The higher the refractive index,

Higher refractive index, thinner lenses, and lighter lenses for a more comfortable wearing experience.

Glass lenses-The main raw material of glass lenses is optical glass. Not easy to scratch, better light transmittance and higher refractive index, the higher the refractive index, the thinner the lens, so the glass sheet is usually thinner. But the glass is fragile and the material is too heavy.

PC lens (polycarbonate lens)-has strong toughness and does not break (2cm can be used for bulletproof glass), so it is also called safety lens; meanwhile, its specific gravity is only 2 grams per cubic centimeter. However, since it is a plastic lens after heating from the solid state, it will be deformed when heated, and it is not suitable for high humidity and heat occasions.

Resin lensformed by chemical synthesis and polishing by using resin as raw material. The lens has light specific gravity, strong impact resistance, good light transmission and low cost, and can meet special needs. However, its surface wear resistance and chemical resistance are worse than glass, its surface is easy to scratch, and its water absorption is greater than glass. At the same time, the thermal expansion coefficient is high, the thermal conductivity is poor, the softening temperature is low, and it is easy to deform and affect the optical performance.

Nylon lensmade of nylon, characteristics: high elasticity, excellent chemical quality, strong impact resistance, when it was invented, it was used as eyeglass protection glasses, and it was widely used in military, police, shooting range and other industries Promotion. However, the wear resistance is worse than glass, and the production cost is high.

Super-tough lenses-Just like PC lenses, they can withstand the falling ball test. However, PC lenses need special edge-grinding machines, while super-tough lenses can be processed by ordinary edge-grinding machines and punching machines. PC is easier.

Take myopia lenses, where the lens diameter is 60mm, which is equivalent to the size of the lens in the frame.

1. The refractive index of resin lenses is lower than that of ordinary glass lenses, so resin lenses of the same degree are thicker.

2. The transmittance of the resin lens is 92%, and the ordinary glass lens with a lower refractive index of 1.523 is more than 2% higher.

3. Resin lenses are very easy to dye, and can be dyed into various colored lenses with different light transmittances, but actually wearing colored lenses for a long time is not good for eye health, because colored lenses are generally made for special groups. Such as photophobia, color blindness, etc.

4. Resin lenses have a lower specific gravity. The same luminosity is 60% of that of 1.523 glass lenses, but high-light lenses are still not comparable to high-fold glass lenses.

5. The resin lens has strong impact resistance. When it is broken by impact, there are fewer fragments, and the fragment area is large and blunt. It reduces the damage to the eyes and face to a minimum.

6. Even if the resin lens is properly maintained, it can only be replaced for a maximum of 2 years. The way to check whether the lens needs to be replaced is to take a piece of black paper as the background, and look at the lens scratches under the incandescent lamp. There are too many scratches. It needs to be replaced. Because glass lenses have good surface hardness, even if worn for 3-5 years, there are few scratches on the lens surface ^[4] .

7. Resin lenses have lower thermal conductivity, so their fog resistance is better than that of ordinary glass lenses. Due to the above characteristics, resin lenses have gradually replaced ordinary low refractive index 1.523 glass lenses.