From incandescent lamps to array spectroradiometers: enabling detector-based traceability for spectral irradiance measurements

The metrological traceability of spectroradiometric measurements across industrial, health, scientific, and environmental sectors has traditionally relied on incandescent lamp-based transfer standards. With the global phaseout of incandescent lamps and their decreasing availability, there is a pressing need to establish an alternative method for disseminating the spectral irradiance unit for spectroradiometric applications. To address this, a detector-based approach utilizing compact, portable array spectroradiometers supported by digital metrological twin as transfer standards has been developed. To support this approach, a dedicated Array Spectroradiometer Characterization (ASC) facility has been established at Physikalisch-Technische Bundesanstalt (PTB), Germany. The ASC facility is designed to implement practical and affordable procedures for the comprehensive characterization of array spectroradiometers with respect to most important instrumental properties such as linearity, pixel-to-wavelength assignment, effective reference plane position and spectral stray light, which are the major sources of measurement uncertainty in spectroradiometric applications of the instruments. The facility has been employed to characterize array spectroradiometers from the ultraviolet to the near-infrared spectral range. The results obtained from these characterizations have been used to demonstrate the suitability of array spectroradiometers as viable detector-based transfer standards for achieving traceability in spectral irradiance measurements. Consequently, the ASC facility contributes to the development of a robust, practical detector-based calibration infrastructure that enhances the reliability of spectroradiometric data for scientific, industrial domains (i.e. solar radiation measurements, actinic radiometry, photovoltaics, lighting, and colour).