In the previous article, we discussed “How much does a pair of sunglasses weigh?”. In this article, let’s talk about 'How Do Sunglasses Work?'.
How Do Sunglasses Work?
Sunglasses can not only prevent uncomfortable strong light but also protect eyes from ultraviolet rays. All of this contributes to the metal powder filter device, which will work when the light goes through it. Colored glasses can selectively absorb some of the wavelengths of the sunlight with the help of very fine metal powders (iron, copper, nickel, etc.). In fact, when the light goes through the lenses, the light is reduced based on the so-called 'destructive interference' process. In other words, when certain wavelengths (UVA, UVB, and sometimes infrared) go through the lenses, they will cancel each other out on the inside of the lenses.
The overlapping of light waves is not accidental. They will cancel each other at that time when the peaks of one wave are combined with the troughs of the adjacent waves. The phenomenon of destructive interference depends on the refractive index of the lenses that is, the degree of deviation when light passes through different substances in the air. And it also depends on the thickness of the lens. Generally speaking, the thickness of the lens is different, and the refractive index of the lens varies according to the difference in chemical composition.
Polarized sunglasses provide another mechanism to protect the eyes. The reflected light from the asphalt road is a relatively special polarized light. The difference between this reflected light and the light directly from the sun or any artificial light source lies in the problem of order. Polarized light is formed by waves that vibrate all the way in one direction, while ordinary light is formed by waves that vibrate non-directionally. It's like a group of people walking in disorder and a group of soldiers marching in order, forming a sharp dialogue. Generally speaking, reflected light is an orderly light. Polarizing lenses are particularly effective in blocking this light because of its filtering properties. This kind of lens allows only polarized waves that vibrate in a certain direction to pass through, just like 'combing' the light.
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