Previtamin D action spectrum: Challenging CIE towards a standard

In 2006, CIE published a technical report on an action spectrum for the production of previtamin D₃ in human skin. CIE procedure is to publish guidelines (e.g., an action spectrum) and let the community test them before moving to define a standard. The CIE previtamin D₃ action spectrum has been in use for 15 years, and challenged on several occasions; a number of alternative action spectra have been suggested. To date (2021) no alternative action spectrum has shown clear advantages over the CIE version when tested against experimental outcomes. Thus, the CIE action spectrum remains widely used, but not fully accepted as best representing the photobiology in human skin leading to synthesis of vitamin D. We report on a CIE workshop designed to address the challenges to the CIE action spectrum, and explore alternative action spectra. The workshop concluded that the CIE action spectrum probably requires amendment, with several candidates for consideration in determining any changes. However, until there is a clear alternative, the CIE action spectrum should remain in use whilst ensuring full spectral information about sources of ultraviolet radiation. Thus, results are comparable between studies and can be recalculated to an updated action spectrum if necessary.