The first set of quantitative data of diffuse erythemal UV and W-A radiatio
n in tree shade at a sub-tropical Southern Hemisphere latitude is presented
. Over the summer, approximately 60% of the erythemal UV radiation in tree
shade is due to the diffuse component. Similarly, approximately 56% of the
UV-A radiation in tree shade is due to the diffuse component. In tree shade
these diffuse UV percentages are relatively constant from the morning to n
oon to afternoon periods. In comparison, in full sun, there is a decrease i
n the percentage of diffuse UV from morning to noon to afternoon. The expos
ures to diffuse UV on a horizontal plane in toe shade between 9:00 EST and
15:00 EST are of the order of 4 MED (minimum erythemal dose)and 14 J cm(-2)
for erythemal UV and UV-A, respectively. The high diffuse UV component in
the shade may result in high UV exposures not only to unprotected parts of
the body on a horizontal plane, but also in equally high UV irradiances to
parts of the body, including the eyes and face, that are not UV protected.
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