มาตราฐาน UV400 สามารถกันได้เฉพาะ UVB และ UVC ส่วน UVA ไม่รับประกันว่าสามารถกันได้ครับ
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Ultraviolet is the invisible part of light, made up of UVA, UVB, and UVC rays. With prolonged exposure to UV, you eye may begin to turn opaque. Ultraviolet light is found between 50 nanometers and 380 nanometers (wavelength of light), whereas visible light is between 381 nanometers and 770 nanometers. The term UV 400 stems from this. It is recommended that you protect yourself from UV radiation up to 400 nanometers, which extends into part of the visible spectrum to ensure complete blockage of ultraviolet light. This is what distinguishes "cheap" sunglasses from more expensive ones. Dime store sunglasses often say that they protect from UV when they really do not. Most will block harmful UVC and UVB rays, but most do not block the most damaging UVA rays. This is why UV 400 is so important. UVA rays are the ones closest to the visible spectrum, and are known to cause cataracts and pterygium at 300 to 380 nanometers. Since most inexpensive sunglasses to do not cover this range, you are still at risk. Thus, it is worth it to spend a little more to guarantee full protection.
http://www.sporteyes.com/sportseye.htm
