Sunglasses, also known as sun visors, are protective eyewear used to block sunlight and reduce eye fatigue and glare. They selectively absorb ultraviolet (UV) and harmful light rays through filtering technology. The core principles include the destructive interference of metal powders and the directional blocking of polarized light by polarizing filters. According to their use, they can be divided into sun visors, light-colored lenses, and special-purpose lenses (for skiing/driving). Polarized lenses can effectively eliminate polarized glare reflected from water and snow.
High-quality products must meet UV protection standards (UV400 label) and transmittance grading requirements (sun visors have a transmittance of 8%-40%). Sunglasses lens types include anti-reflective, polarized, and photochromic lenses. Driving sun visors must meet the national standard of transmittance greater than 75% to ensure nighttime driving safety. When purchasing, pay attention to the uniformity of the lens coating and the optical center deviation to avoid inferior lenses that may cause visual distortion. International standards classify sunglasses into decorative "fashion glasses" and functional "general-purpose glasses," the latter with strict limits on UV blocking rate and refractive error.
