Portable detector‐based primary scale of spectral irradiance

A method developed at the Helsinki University of Technology (HUT) for calibrating standard lamps of spectral irradiance in UV‐A and UV‐B regions is presented. The method is based on a compact filter radiometer that is characterized absolutely to measure spectral irradiance. The filter radiometer can be brought to laboratories where accurate calibrations are needed. The method overcomes some of the instability problems encountered when using lamps as transfer standards, which makes it also useful in intercomparison campaigns. Test measurements are presented where two standard lamps issued by the National Institute of Standards and Technology (NIST), USA, are compared with the HUT scale held by the radiometer. The results suggest that the agreement between the two scales (HUT and NIST) is approximately 1%–2% in the wavelength region from 300 nm to 400 nm.