Can photochromic glasses protect against ultraviolet rays?

Many people know about photochromic glasses, which are also a kind of anti-sun glasses. Photochromic glasses are quite common in life. In summer, ultraviolet rays can cause great harm to the human body. So many people want to know whether photochromic lenses can protect against ultraviolet rays. This also depends on the function of the photochromic lenses.

1. Photochromic mirror

Photochromic lenses can only adjust the brightness of light and have nothing to do with UV protection. Some lens coatings have UV protection functions. Pure photochromic lenses not only cannot protect the eyes but are harmful. However, even with sunglasses, you should not look directly at the sun. Only special lenses, such as those used to observe solar eclipses, can be used to view the sun.

2. Photochromic lenses cannot avoid ultraviolet radiation

Photochromic glasses do not have the function of protecting against ultraviolet radiation, but because the color becomes darker under strong light, they can prevent the irritation of strong light to the eyes. Therefore, wearing these plain photochromic glasses can protect people from the irritation of sunlight, especially those working outdoors under the scorching sun. However, not everyone can wear photochromic glasses. For example, patients with glaucoma should not wear photochromic glasses because the light becomes dim and the pupils tend to dilate, which can induce increased intraocular pressure and cause glaucoma attacks.

3. Color change principle

Photochromic glasses are made by adding a silver halide chemical to ordinary optical lenses, which can turn the lenses into light brown or light gray. Photochromic lenses containing silver halides will decompose into halogen elements and silver ions under strong light. The free silver ions can deepen the color of the lenses. If these lenses are put back into a weak light environment, the halogen elements and silver ions will recombine to make the lens color lighter. In this way, the halogen silver ions continue to combine and decompose, causing the color of the lenses to change shades. This is the secret of the color change of photochromic glasses. Since silver halide is dissolved in the lens when the glasses are manufactured, the color changing period of the lens can be maintained for 2 to 3 years. In other words, the best service life of photochromic glasses is 2 to 3 years. If the color change is not obvious, they should be replaced.