Popular Science: How do color-changing glasses achieve color change when exposed to light？

With the magic of technology, more and more glasses have realized "one mirror and dual purpose": normal optical lenses indoors, and solar lenses outdoors. This is what we call color-changing glasses. Its principle, as the name implies, is that the color of the glasses will change according to the change of light. When we are under strong light or in the sun, the color of this kind of glasses will become darker, thereby protecting the eyes from harm. In the hot sun In summer, as long as we have a pair of color-changing glasses, we can easily deal with the harsh sun.

How is this achieved? Today we will share with you the following science:
The lens of the color-changing glasses is made of a material called "photochromic glass". Since this glass lens was invented in 1964, glasses with this kind of lens have been popular with consumers. Then, this kind of magical glasses is How to change color when seeing light?

Color-changing glasses can change color by light because the lens of this kind of glasses contains silver halide (silver chloride, silver bromide) microcrystals. When it is irradiated by ultraviolet or short wave of visible light, the halogen releases electrons and the electrons are captured by silver ions. Silver ions will be reduced to silver atoms, and silver atoms will absorb light, the transmittance of the lens will decrease, and the color of the lens will become darker; when the light becomes darker, the halogen in the lens reacts reversibly, and the silver and halogen at this time Combined, the lens will return to a transparent or light-colored state.

So, how should we choose when buying color-changing glasses?
First of all, it is necessary to determine the color of the lens and the depth of the lens color according to personal needs, but it should be noted that the color of the two lenses of the color-changing glasses should be the same with no obvious difference in color depth. High-quality color-changing glasses will change color after seeing the sun. Fast, the color fades quickly when the light is dark, and poor-quality color-changing glasses may change color slowly, fade slowly, or do not change color at all.