Lenses are no stranger to many people, and it is the lens that plays a major role in myopia correction and spectacle fitting. There are different types of coatings on lenses, such as green coatings, blue coatings, blue-purple coatings, and even the so-called "local tyrant gold coatings" (a colloquial term for gold-colored coatings). The wear and tear of lens coatings is one of the main reasons for spectacle replacement. Today, let's learn about the knowledge related to lens coatings.
Before resin lenses came into being, glass lenses were the only ones available on the market. Glass lenses have advantages such as high refractive index, high light transmittance, and high hardness, but they also have shortcomings: they are easy to break, heavy, and unsafe, among others.
To address the shortcomings of glass lenses, manufacturers have researched and developed various materials in an attempt to replace glass for lens production. However, these alternatives have not been ideal—each material has its own advantages and disadvantages, making it impossible to achieve a balanced performance that covers all needs. This includes even the resin lenses (resin materials) used today.
For modern resin lenses, coating is an essential process. Resin materials also have many classifications, such as MR-7, MR-8, CR-39, PC, and NK-55-C. There are also numerous other resin materials, each with slightly different characteristics. Whether it is a glass lens or a resin lens, when light passes through the lens surface, several optical phenomena occur: reflection, refraction, absorption, scattering, and transmission.
Anti-Reflective Coating
Before light reaches the surface interface of a lens, its light energy is 100%. However, when it exits the rear interface of the lens and enters the human eye, the light energy is no longer 100%. The higher the percentage of light energy retained, the better the light transmittance, and the higher the imaging quality and resolution.
For a fixed type of lens material, reducing reflection loss is a common method to improve light transmittance. The more light is reflected, the lower the lens's light transmittance, and the poorer the imaging quality. Therefore, anti-reflection has become a key issue that must be addressed for resin lenses—and this is how anti-reflective coatings (also known as anti-reflection films or AR coatings) are applied to lenses (initially, anti-reflective coatings were used on certain optical lenses).
Anti-reflective coatings utilize the principle of interference. They derive the relationship between the light intensity reflectance of the coated lens's anti-reflective layer and factors such as the wavelength of incident light, coating thickness, coating refractive index, and lens substrate refractive index. This design causes the light rays passing through the coating to cancel each other out, reducing light energy loss on the lens surface and improving imaging quality and resolution.
Most anti-reflective coatings are made from high-purity metal oxides such as titanium oxide and cobalt oxide. These materials are applied to the lens surface through an evaporation process (vacuum evaporation coating) to achieve an effective anti-reflective effect. Residues often remain after the anti-reflective coating process, and most of these coatings exhibit a greenish hue.
In principle, the color of anti-reflective coatings can be controlled—for example, they can be manufactured as blue coatings, blue-purple coatings, purple coatings, gray coatings, etc. Coatings of different colors differ in terms of their production processes. Take blue coatings as an example: blue coatings require controlling a lower reflectance, making their coating process more difficult than that of green coatings. However, the difference in light transmittance between blue coatings and green coatings may be less than 1%.
In lens products, blue coatings are mostly used in mid-to-high-end lenses. In principle, blue coatings have higher light transmittance than green coatings (it should be noted that this is "in principle"). This is because light is a mixture of waves with different wavelengths, and the imaging positions of different wavelengths on the retina vary. Under normal circumstances, yellow-green light is imaged exactly on the retina, and green light contributes more to visual information—thus, the human eye is more sensitive to green light.
Post time: Nov-06-2025