ERYTHEMAL IRRADIANCES OF FILTERED ULTRAVIOLET-RADIATION

A spectrum evaluator (3 cm x 3 cm) employing four passive dosimeters h as been used to evaluate the time averaged spectrum to allow calculati on of the erythemal exposures resulting from the predominantly UVA com ponent of filtered solar ultraviolet radiation. An exposure interval o f approximately 20 min to autumn and spring sunshine was required for the spectrum evaluator to allow evaluation of the filtered source spec trum. For a clear spring day an erythemal exposure of 0.85 MED (minimu m erythemal dose) to a horizontal plane and 0.38 MED to a vertical pla ne over a 6 h period was measured within a glass enclosure. For a part ially cloudy day six weeks later, these were 0.89 and 0.44 MED for the horizontal and the vertical planes respectively. The ratios of the fi ltered to the unfiltered erythemal exposures within and outside the en closure respectively ranged from 0.08 to 0.18 throughout the two days.