Sunglasses, also called sun-shading mirrors, are used for shading. People usually adjust the luminous flux by adjusting the pupil size in the sun. When the light intensity exceeds the adjustment ability of the human eyes, it will cause damage to the human eyes.
Therefore, in outdoor activities, especially in summer, it is necessary to use sun-shading mirrors to block the sun to reduce fatigue caused by eye adjustment or damage caused by strong light stimulation.
Sunglasses can block uncomfortable glare, and at the same time protect the eyes from ultraviolet rays. All this is due to the metal powder filter, which can “select” the light when it hits it. Colored glasses can selectively absorb some of the wavelengths that make up the sun’s rays because they use very fine metal powders (iron, copper, nickel, etc.). In fact, when light hits the lens, the light is reduced based on the so-called “destructive interference” process. In other words, when certain wavelengths of light (herein referred to as ultraviolet a, ultraviolet b, and sometimes infrared) pass through the lens, they will cancel each other out on the inside of the lens, which is toward the eye. The overlapping of light waves is not accidental: the peaks of one wave and the troughs of the adjacent waves combine to cancel each other. The phenomenon of destructive interference depends on the refractive index of the lens (that is, the degree of deviation when light passes through different substances in the air), and also depends on the thickness of the lens. Generally speaking, the thickness of the lens does not change much, and the refractive index of the lens varies according to the difference in chemical composition. And the sunglasses should not be directly exposed to the sun.
Polarized sunglasses wearing effect
Polarized sunglasses provide another mechanism for eye protection. The reflected light from the asphalt road is 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 in one direction, while ordinary light is formed by waves that vibrate non-directionally. This is like a group of people walking in disorder and a group of soldiers marching in order. , Formed a sharp contrast. Generally speaking, reflected light is an orderly light. Polarized lenses are particularly effective in blocking this light because of their filtering properties. This kind of lens allows only polarized waves that vibrate in a certain direction to pass through, just like “combing” light. For road reflection problems, the use of polarized glasses can reduce light transmission, because it does not let light waves that vibrate parallel to the road pass. In fact, the long molecules of the filter layer are oriented in the horizontal direction and can absorb horizontally polarized light. In this way, most of the reflected light is eliminated, and the entire illuminance of the surrounding environment is not reduced, and the polarizer can face the sun directly.
Color changing glasses
The lenses of color-changing glasses can darken after the sun’s rays hit. When the lighting diminished, it became bright again. This is possible because the silver halide crystals are working. Under normal circumstances, it can keep the lens perfect transparency. Under the sunlight, the silver in the crystal separates, and the free silver forms small aggregates inside the lens. These small silver aggregates are irregular blocks of canine teeth. They cannot transmit light, but can only absorb light. As a result, the lens darkens. When the light is dark, the crystal re-forms, and the lens returns to its bright state.