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Nowadays, the pandemic situation caused by the COVID-19 virus inspired many companies, research institutes and lighting designers to adopt UV radiation as a new tool in their projects and research. The promising germicidal effect of the UV-C radiation, also on the Coronavirus, raises the question of the reliable measurement of the UV radiation. However, this complex task needs an expertise and appropriate equipment. The system suitable for UV measurements consists of a high-precision spectroradiometer with stray light correction and irradiance probes or PTFE-coated integrating spheres for total radiant flux measurements. However, the reliable and traceable calibration of the system is the challenging factor. So far, no national metrological institute has been able to offer a reference standard for the total radiant flux in the UV-B and UV-C spectral region. Therefore, we have realized traceable UV LED calibration standards, which complete measurement system for UV radiation presented here. The UV LED calibration standards have been developed for the typical peak wavelengths of 280 nm (UV-C), 305 nm (UV-B) and 365 nm (UV-A). The traceability of the radiant flux is ensured by the precise calibration of the spectroradiometer with the irradiance probe and a subsequent integrative measurement using a goniospectroradiometer. Such UV LED calibration standards can be used for monitoring and for absolute calibration of UV measurement equipment consisting of the stray light corrected spectroradiometer and the integrating sphere. The largest contribution to the measurement uncertainties of the systems containing integrating spheres is the fluorescence of the coating material. Special manufacturing procedure with optically pure Polytetrafluorethylen (PTFE) enabled us to produce new integrating spheres with permanently low fluorescence.
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