Cloud and the solar zenith angle (SZA) influence the magnitude of the diffuse erythemal UV. The aim of this research was to investigate the variation of the short wavelength cut-off and the maximum spectral irradiance wavelength for the diffuse spectral erythemal UV. The diffuse spectral solar UV was measured on a horizontal plane at ten minute intervals over a four month period with a UV spectroradiometer for the SZA range of 4.1 to 80 degrees. The short wavelength cut-offs and the maximum spectral irradiance wavelengths of the diffuse erythemal UV did not change significantly with cloud cover. The short wavelength cut-off was influenced by SZA and ranged from 290.5 ± 0.3 nm for the small SZA to 295.1 ± 0.7 nm for the larger SZA. The maximum spectral irradiance wavelength of the diffuse erythemal UV was not influenced significantly for SZA of 40 degrees or less. For higher SZA, the maximum spectral irradiance wavelength of the diffuse erythemal UV increased from 305 nm to 313.9 nm
