Responsivity calibration methods for 365 nm irradiance meters

Two detector-based responsivity calibration methods have been compared at the National Institute of Standards and Technology (NIST) for UV irradiance meters in the 365 nm spectral region. Both methods are based on an electrical substitution High Accuracy Cryogenic Radiometer (HACR), but utilize different facilities and transfer standards. One facility is a monochromator-based, spectral power responsivity measuring system utilizing an aperture scanning method, while the second is a tunable laser and integrating sphere source system using a light-trapping silicon transfer detector with a known aperture area. The first comparison by NIST of these two fundamentally different methods agreed to 1% to 2% near the peak and long wavelength side of the bandpass curves which is comparable to their expanded (k=2) uncertainties.