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A UV index reading of 3 to 5 means moderate risk of harm from unprotected sun exposure. Stay in shade near midday when the sun is strongest. If outdoors, wear sun-protective clothing, a wide-brimmed hat, and UV-blocking sunglasses. Generously apply broad spectrum SPF 50+ sunscreen every 1.5 hours, even on cloudy days, and after swimming or ...
Medical experts advise the public on the importance of wearing sunglasses to protect the eyes from UV; [26] for adequate protection, experts recommend sunglasses that reflect or filter out 99% or more of UVA and UVB light, with wavelengths up to 400 nm. Sunglasses that meet this requirement are often labeled as "UV400".
The WHO-standard ultraviolet index is a widely publicized measurement of total strength of UV wavelengths that cause sunburn on human skin, by weighting UV exposure for action spectrum effects at a given time and location. This standard shows that most sunburn happens due to UV at wavelengths near the boundary of the UVA and UVB bands.
Once inside, away from the triggering UV light, the cold lenses take longer to regain their transparency than warm lenses. A number of sunglass manufacturers and suppliers including INVU, BIkershades, Tifosi, Intercast, Oakley , ZEISS , Serengeti Eyewear , and Persol provide tinted lenses that use photochromism to go from a dark to a darker state.
UV-B, predominantly responsible for the harmful effects of sunlight, poses the highest risk for erythema, photokeratitis, sunburn and skin cancer. [16] [17] [18] While longer UV-C wavelengths and UV-A can also cause damage, their effects are less severe than UV-B. In contrast, far-UVC has shown remarkably different results.
Photokeratitis can be prevented by using sunglasses or eye protection that transmits 5–10% of visible light and absorbs almost all UV rays. Additionally, these glasses should have large lenses and side shields to avoid incidental light exposure. Sunglasses should always be worn, even when the sky is overcast, as UV rays can pass through ...