Erythemal irradiances of filtered ultraviolet radiation

Abstract

A spectrum evaluator (3 cm x 3 cm) employing four passive dosimeters has been used to evaluate the time averaged spectrum to allow calculation of the erythemal exposures resulting from the predominantly UVA component of filtered solar ultraviolet radiation. An exposure interval of approximately 20 minutes to autumn and spring sunshine was required for the spectrum evaluator to allow evaluation of the filtered source spectrum. For a clear spring day an erythemal exposure of 0.85 MED to a horizontal plane and 0.38 to a vertical plane over a six hour period was measured within a glass enclosure. For a partially cloudy day six weeks later, these were 0.89 MED and 0.44 MED for the horizontal and the vertical planes respectively. The exposure is predominantly due to the UVA component of the solar radiation. The ratios of the filtered to the unfiltered erythemal exposures within and outside the enclosure respectively ranged from 0.08 to 0.18 throughout the two days.