First Comparison of the Solar and an SI Radiometric Scale

The paper presents the results of the first comparison between the solar radiometric scale, the World Radiometric Reference (WRR) and a Système International radiometric scale (SI scale) as disseminated by national standards laboratories, in particular, the scale based on the cryogenic radiometer of the National Physical Laboratory (NPL). The comparison used a number of transfer standards to act as intermediaries between the two scales which limited the overall uncertainty to 0,07%. The final result shows that the WARR and the NPL SI scale agree to better than 0,03%, well within the absolute uncertainty of the two scales.