In previous studies conducted in our lab, we have been investigating the aging effects on sunglasses. Some preliminary results have been indicating changes on the UV protection on the lenses. Therefore, besides irradiating the samples with a proper sun simulator, we have also been concerned on exposing the sunglasses to natural sun for further investigation and comparisons. Thus, this project aims expose the lenses for 24 months using an automatic solar exposition station, which consists of a series of 5 panels, housing 60 lenses arranged in the vertical position to the ground, which will be irradiated by the sun from sunrise until sunset. A box structure moves along a rail, driven by a motor and then the lenses are exposed. Humidity, rain, temperature, dust and UV index sensors, as well as a video camera are part of the system. The exposure time and UV index will be recorded and automatic opening or closing the box system may also be controlled by a PC using a webserver. The system was tested in working conditions, i.e. exposed to the weather and being automatically controlled, for five months to certifying that the samples could be exposed without being damaged. The next step of the research is to start the exposition cycles and to measure the expected transmittance variations after each cycle.
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.
The International Commission on Non-Ionizing Radiation Protection (ICNIRP) establishes that the safe limits regarding ultraviolet radiation exposure in the spectral region 180nm–400nm incident upon the unprotected eye(s) should not exceed 30 Jm-2 effective spectrally weighted (spectral weighting factors are provided by ICNIRP); and the total (unweighted) ultraviolet radiant exposure in the spectral region 315nm–400nm should not exceed 104 Jm-2. However, it should be considered that the spectral range from 180nm–280nm does not reach the surface of the Earth, since it is absorbed by the ozone layer of the atmosphere. The Brazilian Standard for sunglasses protection, NBR15111(2004), as well as the British Standard BSEN1836(2005) and American Standard ANZI Z80.3(2009), requires the UV protection in the spectral range 280nm–380nm, but does not take into account the total (unweighted) UVA radiant exposure. These limits are discussed in this work and calculations have been made for 27 state capitals of Brazil to understand the limits that should be involved in order to protect the eyes of the Brazilian population. These calculations and considerations may be extended to other countries as well. As a conclusion, we show that the upper limit for the UVA protection of 400nm should be included in the Brazilian standard, as well as the irradiance limits. Furthermore, the parameters for the resistance to irradiance test required on the Brazilian standard are also discussed herein as well the significance of this test. We show that the test should be performed by the sun simulator for a longer period than currently required.