title: Horizontal and sun-normal spectral biologically effective ultraviolet irradiances.
abstract: The dependence of the spectral biologically effective solar UV irradiance on the orientation of the receiver with respect to the sun has been determined for relatively cloud-free days at a sub-tropical Southern Hemisphere latitude for the solar zenith angle range 35-64 degrees. For the UV and biologically effective irradiances, the sun-normal to horizontal ratio for the total UV ranges from 1.18 +/- 0.05 to 1.27 +/- 0.06. The sun-normal to horizontal ratio for biologically effective irradiance is dependent on the relative effectiveness of the relevant action spectrum in the UV-A waveband. In contrast to the total UV, the diffuse UV and diffuse biologically effective irradiances are reduced in a sun-normal compared with a horizontal orientation by a factor ranging from 0.70 +/- 0.05 to 0.76 +/- 0.03.
authors.affiliation: Centre for Astronomy and Atmospheric Research, University of Southern Queensland, Toowoomba, Australia. parisi@usq.edu.au
authors.forename: A V
authors.initials: AV
authors.lastname: Parisi
authors.forename: M G
authors.initials: MG
authors.lastname: Kimlin
mesh_terms: D006801:Humans; D010944:Plants / Q000528:radiation effects; D011874:Radiometry; D013056:Spectrophotometry, Ultraviolet; D013472:Sunlight; D014466:Ultraviolet Rays