UV-resistant sunglasses are because a special coating film is added to the lens, and the inferior sunglasses can not only block the ultraviolet rays, but also cause the lens transmittance to be seriously reduced, so that the pupils become larger, and the ultraviolet rays will inject a large amount, causing damage to the eyes. How to judge whether sunglasses are UV-resistant?
Method 1. Look at the label of the sunglasses
Obvious signs such as "UV protection" and "UV400" are seen on UV-resistant sunglasses labels or lenses. The "UV index" is also the effect of filtering out ultraviolet rays, which is a very important criterion for purchasing sunglasses. Light with a wavelength between 286 nm and 400 nm is called ultraviolet light. Generally, a 100% UV index is impossible. Most sunglasses have a UV index between 96% and 98%.
Sunglasses with UV protection are generally indicated in the following ways:
a) marked "UV400": this means that the cut-off wavelength of the lens to ultraviolet is 400nm, that is, its maximum value τmax (λ) of the spectral transmittance of the wavelength (λ) below 400nm is not more than 2%;
b) marked "UV", "anti-ultraviolet": this means that the cut-off wavelength of the lens to ultraviolet is 380nm, that is, its maximum value τmax (λ) of the spectral transmittance of the wavelength (λ) below 380nm is not more than 2%;
c) Label "100% UV absorption": This means that the lens has a 100% absorption of UV light, ie its average transmittance in the UV range is no more than 0.5%.
Sunglasses that meet the above requirements are sunglasses that are truly UV-protective.