Exposures to UVA radiation (320 − 400 nm) have been linked to increasing the risk of skin cancer, premature skin photoageing and skin wrinkling. The relative proportion of the UVA irradiances in the solar spectrum changes with time of day and season. Material such as window glass found in offices, homes and motor vehicles acts as a barrier to the shorter solar UVB wavelengths (280 - 320 nm) and transmits some of the longer UVA wavelengths (dependent on the type of glass). As a result, the spectrum of the filtered UV transmitted through the material may be substantially different from that of the unfiltered solar UV spectrum. This results in a change in the relative ratio of UVA to UVB irradiances and a consequent change in the biologically damaging UV exposures. For these environments where the UVB wavelengths have been removed and the UVA wavelengths are still present, it is necessary to consider the erythemal irradiances due to these UVA wavelengths only. This paper investigates the times taken for an exposure of 1 SED (standard erythemal dose) due to the UVA wavelengths.
A prototype UVA dosimeter that is responsive to the UVA wavelengths only has been developed for measurement of personal exposures. The chemical phenothiazine, cast in thin film form and which is responsive to both the UVA (320-400 nm) and UVB (280-320 nm) part of the spectrum was used and filtered with mylar. This combined system responded to the UVA wavelengths only and underwent a change in optical absorbance as a result of UVA exposure. The wavelength of 370 nm was employed for quantifying the change in optical absorbance of the combined mylar/phenothiazine dosimeter and a calibration curve determined for measuring the UVA exposures. UVA exposures to approximately 50 J cm<sup>-2</sup> may be measured prior to saturation of the response.
Polysulphone has been widely used as a dosimeter to quantify personal solar UV exposures to humans during normal daily activities. In summer at sub-tropical and tropical latitudes, the dynamic range for UV exposures allows the use of the polysulphone to measure solar UV over periods of approximately three to six hours. The use of mesh as a filter over the polysulphone has been previously reported to extend the dynamic range. In this paper the use of a simple filter that is incorporated as part of the dosimeter is reported. The dynamic range of the polysulphone was significantly extended with the incorporation of the filter by a factor of approximately four to five.