Wearing sunglasses not only blocks the harsh glare, but also protects the eyes from the UV rays. It is also a fashion. Sunglasses sold in outside shopping malls are sold under the slogan of UV-protective sunglasses. Then the problem is coming. What kind of sunglasses can really be called UV-resistant sunglasses?
UV protection standard unit for UV protection glasses: UV. UV is an abbreviation for English Ultraviolet Rays. Ultraviolet light belongs to invisible light (also called electromagnetic radiation), and the spectrum shows that the ultraviolet wavelength is below 400nm. I don’t know when you buy sunglasses in the store, you notice that there are not many UV-resistant glasses that have a UV400 mark. This is the UV-proof level of the glasses. The UV400 rated glasses indicate 100% UV protection (this is through Special lens coating technology applied to the lens).
The reason why sunglasses can block ultraviolet rays is because a special coating film is added to the lens to block and absorb ultraviolet rays, and also block a part of visible light, so that the transmittance of the lens is reduced. Therefore, the ability of high-quality sunglasses to block ultraviolet rays is strong, and the transmittance is not much decreased, and the coating film has a certain hardness and is not easy to wear.
To distinguish whether a pair of sunglasses has the function of preventing ultraviolet rays, obvious marks such as "anti-ultraviolet" and "UV400" can be seen on the labels or lenses of some products. 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 286nm and 400nm is called ultraviolet light. Generally, a 100% UV index is impossible. Most sunglasses have a UV index between 96% and 98%.
The sunglasses labeled "UV400" can achieve a level of defense against more than 90% of the ultraviolet rays, and the lenses are specially processed to block ultraviolet rays with a wavelength of less than 400nm. Those who wear contact lenses can choose contact lenses with UV protection, can filter out 90% of UV rays, and then wear sunglasses, the safety level is even higher.
When choosing sunglasses, in addition to its UV protection, check the diopter of the lens. At this point, you can put the sunglasses back and forth in front of your eyes. If the object and the lens move together, it means that the lens has diopter, which will be bad for the eyes. In addition, it is necessary to check the smoothness of the surface of the lens. If the surface of the lens is not smooth, the external object will be deformed and distorted, causing the eyeball to swell and appear visual fatigue symptoms such as nausea, forgetfulness and insomnia.