Realization of the New Candela (1979) at NRC

The paper describes the realization of a new scale of luminous intensity at the National Research Council of Canada, based on the 1979 redefinition of the candela. Two different methods were used. In the first method, the lamps were calibrated directly by means of absolute radiometers equipped with V (λ)-correcting filters. In the second method, secondary radiometers incorporating silicon photodiodes were first calibrated spectrally by means of absolute radiometers, then used in conjunction with V (λ) filters to calibrate the lamps. The sources of error and measurement results for the two methods are analyzed in detail. A comparison of the new scale with the previous platinum-blackbody-based scale indicates that the new NRC candela is 1.2% smaller on average than the old NRC candela.