How to choose and wear sunglasses
sunglasses generally divided into two major categories of light and dark, is made up of many colors. Evaluating the quality of the sunglasses, the emphasis should be the inspection focus and prism degrees, transmittance characteristics, surface quality and internal fault, assembly accuracy and several technical indexes such as cosmetic requirements.
a pair of good quality sunglasses can have the effect of shading and decorative appearance. But, in the market situation is not optimistic. Some vendors cynical, taking advantage of the consumers don't know much about the quality of sunglasses, the use of inferior materials, cheap Windows or other inferior materials of glasses. The material uniformity is poor, containing impurities such as stripe, bubble, can't keep out ultraviolet ray, does not conform to the human physiological requirements. What's more, using visible light transmittance is extremely low, but high uv transmittance of inferior plastic sunglasses, cause harm to consumers.
how to choose and wear sunglasses? The expert warns customer, must not only pay attention to the design of sunglasses, more attention should be paid to its inherent quality. Qualified sunglasses, wavelength at 315 nm to 380 nm long wave ultraviolet transmittance shall not exceed 10%, at 280 nm to 315 nm wavelength uvb rays transmittance should be zero. Wearing sunglasses, so as to make the eyes of the cornea, crystal and retina from damaging ultraviolet rays. Some cheap sunglasses not only can not filter out ultraviolet ray, it will hide because the visible light, after the ultraviolet irradiation is more significant, this kind of inferior than don't wear sunglasses.
sunglasses belong to light series. According to the regulations of the national standard, sunglasses only allows more with diopter of plus or minus 8 degrees, more than the error range is not qualified products. According to scientific research personnel of sunglasses on the market testing, nearly thirty percent of sunglasses diopter over tolerance, some even as high as more than 20 degrees. Experts point out that normal sight consumers put on the sunglasses, like wearing a pair of myopia or hyperopia mirror, after a summer, consumers will be inferior sunglasses & # 8220; Training & # 8221; In patients with nearsightedness or farsightedness. When you wear sunglasses appear the symptom such as dizziness, nausea, distracting, should immediately stop wearing.