Realization of photometric base unit of candela traceable to cryogenic radiometer at UME

At National Metrology Institute of Turkey (UME, Ulusal Metroloji Enstitusu), luminous intensity unit of candela was realized using detector-based approach and photometric scale was re-established depending on this new realization. Candela was measured on photometric bench using interferometric distance measurement system and filter-radiometer traceable to UME primary level electrical-substitution cryogenic radiometer. Thermally stabilized filter radiometer, which has been designed for spectral irradiance measurements, is consists of trap detector, filter housing and precision aperture. Different measurement techniques were used to fully characterize each parameter of filter-radiometer; like effective aperture area, spectral transmittance of V (lambda) filter and responsivity of trap detector.