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The goal of solar ultraviolet (UV) simulation is to reproduce the natural solar UV spectrum. However, this spectrum changes continuously depending on parameters, such as latitude, season, time, cloudiness, etc. From spectra recorded worldwide throughout the year, a realistic ("standard") solar UV spectrum at Earth level was defined by the Deutsches Institut f|r Normung e.V. (DIN) to represent a "worst" case situation. Exposure of human skin to such a spectrum is likely to result in intense biological effects. Simulated solar UV spectra should match the standard spectrum as closely as possible. Here, we present a method to assess the match between a laboratory spectrum and the standard spectrum. Representative UV sources such as xenon arcs, metal halide lamps and fluorescent tubes, along with various filters, have been measured. Differences between the relative irradiance of UV candidate spectra and the standard are calculated for each wavelength. These differences are squared and summed. The lower the sum, the better the match of the source spectrum to the standard sun. This method may be used with or without biological weighting by an action spectrum. We have selected the erythema action spectrum to assess and rank candidate sources. Our analysis shows that filtered ultraviolet B fluorescent tubes are the worst way of simulating solar radiation, with and without weighting by the erythema action spectrum. UV spectra from solaria equipped with combinations of ultraviolet A and ultraviolet B fluorescent tubes are also far from satisfactory. In general, metal halide lamps rank slightly better than the fluorescent UVB tubes. The choice of UV filter plays a significant role in the compliance of candidate UV source. In conclusion, the suggested method allows the determination of the most appropriate UV source to simulate real solar exposure for any targeted biological damage.

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