Turnbull, D. J. and Parisi, A. V. Optimizing Solar UV-Radiation Exposures for Vitamin D3: Comparing Global and Diffuse Spectral UV Radiation. Radiat. Res. 169, 344–349 (2008).

Currently, there is a major gap in the knowledge that is needed to optimize the beneficial effects related to ultraviolet (UV) radiation at wavelengths that induce vitamin D3 synthesis (UVD3) compared to reducing the biologically damaging overexposure to UV radiation. The aim of this study was to investigate the use of diffuse (radiation that is scattered from all directions) UV radiation to optimize exposures to UVD3 radiation and maximize the reduction of exposure to UVA radiation. Data on global and diffuse solar UV-radiation spectra were collected at 10-min intervals in the Southern Hemisphere in the late spring and summer from 1 November 2006 to 28 February 2007. For a solar zenith angle (SZA) of approximately 5°, the observed maximum UVD3 irradiances were 0.80 W/m2 and 0.46 W/m2 for global and diffuse UV radiation, respectively. The observed maximum UVA irradiances were 79.0 W/m2 and 36.2 W/m2 for global and diffuse UV radiation, respectively. For diffuse UV radiation, the maximum ratio of vitamin D3 to UVA radiation was 1.75% at a SZA of approximately 10°, whereas the maximum ratio for global UV was 1.27% at 10°. For SZAs of 25° and less, more UV radiation is in the wavelength region contributing to vitamin D3 synthesis (UVD3) than in the UVA region for diffuse UV radiation than for global UV radiation.

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