Diffuse Component of the Solar Ultraviolet Radiation in Tree Shade

This paper has provided the first set of quantitative data of diffuse erythemal UV and UVA in tree shade at a sub-tropical Southern Hemisphere latitude. Over the summer, approximately 60% of the erythemal UV radiation in the tree shade is due to the diffuse component. Similarly, approximately 56% of the UVA radiation in the tree shade is due to the diffuse component. In the tree shade these diffuse UV percentages are relatively constant from the morning to noon to afternoon periods. In comparison, in full sun, there is a decrease in the percentage diffuse UV from morning to noon to afternoon. The exposures to diffuse UV on a horizontal plane in the tree shade between 9:00 EST to 15:00 EST were of the order of 4 MED and 14 J cm for erythemal UV and UVA respectively. The high diffuse UV component in the shade may result in high UV exposures to not only parts of the body on a horizontal plane that are not protected, but also, equally high UV irradiances to parts of the body, including the eyes and face, that are not UV protected.