Comparison of the biologically effective UV in the shade for three action spectra

Abstract

[Abstract]: There have been numerous studies associated with the measurement of biologically effective UV (UVBE) irradiances for the solar zenith angles (SZA) observed during summer. However, only a small amount is known about UVBE levels related to the larger SZA seen during the autumn and winter months. Spectral UV irradiance measurements were made under clear sky conditions at a sub-tropical Southern Hemisphere site. Biologically effective UV levels for fish melanoma, DNA damage and cataract induction was investigated beneath four specific shade settings, for relatively cloud-free sky conditions and changing solar zenith angle (SZA) between 33o to 63o. The biologically damaging UV in the shade was significant for fish melanoma. Compared to that in full sun, the UVBE associated with DNA damage, cataract and fish melanoma were at levels of approximately 76, 78 and 65% respectively, beneath the shade umbrella. DNA damage, cataract and fish melanoma irradiance levels in the shade of a northern facing covered veranda were significantly less than those beneath the shade umbrella, with levels of approximately 19, 19 and 15% respectively. Although no action spectrum exists for human melanoma and cataract development, the fish melanoma and porcine cataract action spectra may provide an indication of the effective wavelengths. The relative UVBE in the shade compared to full sun depends on the action spectrum that is being considered. The reduction in the UVBE for the different action spectra is not related to the reduction in the unweighted total UV. Shade is important as a UV minimisation strategy, but for long periods, shade alone does not provide enough protection from some biologically damaging UV.