The short wavelength cut-off (λc), the wavelength of the maximum spectral UV (λMax) of spectral pre-vitamin D3 effective solar UV irradiance (UVD3), and the spectral erythemal UV (UVEry) were compared at 5-min intervals over a 6-month period at solar zenith angles (SZA) ranging from 4.7° to 80°. Averaged over the entire period, λc for UVD3 is higher by 1.05 nm than that for UVEry.
The λMax is higher for UVD3 compared to UVEry for SZA < ~50°. For higher SZA (>55°), the ratio of λMax for UVD3 to that for UVEry is less than 1. As the erythemal action spectrum extends into the UVA, the ratio of UVD3 to UVEry irradiances decreases with increasing SZA, along with a decrease in the ratio of λMax for UVD3 compared to UVEry.
The changes in λc and λMax influence both personal UVD3 and UVEry exposure and, to take this into account, a dual calibration technique for polysulphone dosimeters has been developed to simultaneously provide measurements of both types of exposure.
Parisi, A.V., Turnbull, D.J. and Turner, J., 2009. Comparison of biologically effective spectra for erythema and pre-vitamin D3 synthesis. International journal of biometeorology, 53(1), pp.11-15.
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