I. The Principle of Photochromic Lenses
In modern society, as air pollution worsens and the ozone layer is gradually damaged, eyeglasses are often exposed to UV-rich sunlight. Photochromic lenses contain microcrystals of photochromic agents—silver halide and copper oxide. When exposed to strong light, silver halide decomposes into silver and bromine; the tiny silver crystals formed in this process turn the lenses dark brown. When the light fades, silver and bromine recombine into silver halide under the catalytic action of copper oxide, lightening the lenses again.
When photochromic lenses are exposed to ultraviolet (UV) rays, their coating immediately darkens while blocking UV penetration, significantly preventing UVA and UVB from harming the eyes. In developed countries, photochromic lenses have long been recognized by health-conscious consumers for their health benefits, convenience, and aesthetics. Annual growth in the number of consumers choosing photochromic lenses has reached double digits.
II. Color Changes of Photochromic Lenses
On sunny days: In the morning, the air has thin cloud cover, which provides less UV blocking, allowing more UV rays to reach the ground. As a result, photochromic lenses darken more significantly in the morning. In the evening, UV intensity weakens—this is because the sun is farther from the ground, and the mist accumulated during the day blocks most UV rays. Therefore, the lenses’ tint becomes very light at this time.
On cloudy days: UV rays can still reach the ground with considerable intensity at times, so photochromic lenses will still darken. Indoors, they remain nearly transparent with little to no tint. These lenses provide optimal UV and glare protection in any environment, adjusting their color promptly based on light conditions. While safeguarding eyesight, they offer all-around eye health protection anytime, anywhere.
Relationship with temperature: Under the same conditions, as temperature rises, the tint of photochromic lenses gradually lightens; conversely, when temperature drops, the lenses darken slowly. This explains why the tint is lighter in summer and darker in winter.
The speed of color change and the depth of tint also have a certain correlation with lens thickness.
Post time: Aug-28-2025