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28 February 2014UV protection for sunglasses: revisiting the standards
In a continuing work of establishing safe limits for UV protection on sunglasses, we have estimated the incident UV radiation for the 280 nm – 400 nm range for 5500 locations in Brazil. Current literature establishes safe limits regarding ultraviolet radiation exposure in the spectral region 180nm–400nm for weighted and unweighted UV radiant exposure. British Standard BSEN1836(2005) and American Standard ANZI Z80.3(2009) require the UV protection in the spectral range 280nm–380nm, and The Brazilian Standard for sunglasses protection, NBR15111(20013), currently requires protection for the 280nm – 400nm range as established by literature. However, none of them take into account the total (unweighted) UVA radiant exposure.Calculations of these limits have been made for 5500 Brazilian locations which included the geographic position of the city; altitude, inclination angle of the Earth; typical atmospheric data (ozone column; water vapor and others) as well as scattering from concrete, grass, sand, water, etc.. Furthermore, regarding UV safety for the ocular media, the resistance to irradiance test required on this standard of irradiating the lenses for 25 continuous hours with a 450W sunlight simulator leads to a correspondence of 26 hours and 10 minutes of continuous exposure to the Sun. Moreover, since the sun irradiance in Brazil is quite large, integrations made for the 280-400 nm range shows an average of 45% of greater ultraviolet radiant exposure than for the 280-380 nm range. Suggestions on the parameters of these tests are made in order to establish safe limits according to the UV irradiance in Brazil.