About Anti-Reflect Coating

Looking at things across things will make it clearer; this is the advantage of coating. Xcube’s sunglasses have a multi-layer coating on the lens that can be used to harden the lens, making it less prone to scratching, antistatic, oil and water. One of the things that many people often hear but don’t understand is the anti-reflective Coating.

Before explaining the anti-reflective coating, we must talk about the concept of light reflection first. Any object has a refractive index of light. For example, from air to glass lens, it is from refractive index 1 to 1.5, the higher the difference in refractive index between the two sides, the more reflection. The reflected light is easily offset by the other light entering the glasses, so the optical is slightly worse.


But how to reduce the reflection of light? Reducing the refractive index difference is simple way to do. If a layer with 1.38 index is added between the refractive index of 1 and 1.5, the problem of light refraction will be greatly reduced. The 1.38 medium of the layer is called anti-reflection coating. To put it simply, the conservation of energy is used, and the energy of the received light is constant. When the reflected light is reduced, the transmitted light is increased, thus increasing the contrast of the object seen.


However, these films are generally not perfect for anti-reflection. Almost all of the light in a specific frequency wave is not anti-reflective, so that the specific frequency waves of light appear on the lens. Because the wavelength of the reflected light can be determined by the thickness of the film. Blue is called blue film, green is called green film, yellow is called gold film, purple is called purple film.


An interesting point here is that these coatings are anti-reflective films, but often because of the anti-reflective coating, a reflection of one color is found on the lens. In fact, it is not the extra reflected light, but the remaining reflected light. For example, the original reflected light is 300~750nm, but most of the light below 500nm and above 600nm can pass smoothly, after the light of 500~600nm is reflected, we will see green again on the film surface.


In some cases, except for the outer layer, which will be coated, the inner layer will usually be green coated. When all the light can pass smoothly, only the green part of the light can not pass through the lens, the contrast of the visual field will be relatively deeper, which will give people a more clear illusion. That is the contrast has been strengthened rather than being clearer.


The advantage of this is that it will make people's contrast stronger, but it is still a small shortcoming. In addition to increasing the cost, there is the full-band that was originally reflected. When there is only green reflection, some people will not get used to it. Feeling a little bit of weird because there has color left. This is the phenomenon known as ghosting. It's usually just a matter of habit, because in theory the light that is left after the reflection is reduced is weaker than the light without the AR coating.


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