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.