Comparison of biologically effective spectra for erythema and pre-vitamin D3 synthesis

Abstract

This paper has compared the short wavelength cut-off and the wavelength of the maximum spectral UV of the spectral pre-vitamin D3 effective solar UV irradiances (UVD3) and the spectral erythemal UV (UVEry) at five minute intervals over a six month period for the range of solar zenith angles (SZA) from 4.7o to 80o. Averaged over the entire period, the short wavelength cut-off for the UVD3 is higher by 1.05 nm than that for UVEry. The maximum spectral UV is higher for the UVD3 compared to the UVEry for SZA less than approximately 50o. For higher SZA (>55°), the ratio of the maximum spectral UV for UVD3 to that for UVEry is less than one. As the erythemal action spectrum extends into the UVA, the ratio of the UVD3 to UVEry irradiances decreases with increasing SZA, along with the decrease in the ratio of the maximum spectral UV for UVD3 compared to UVEry. The changes in short wavelength cut-off and maximum spectral UV influence the respective exposures and to take this into account, a dual calibration technique for polysulphone dosimeters has been developed to simultaneously provide both the personal UVD3 exposures and the UVEry exposures.