Responsivity calibrations of trap detectors with a cryogenic absolute radiometer and a power-stabilized 543.516-nm He-Ne laser are described. The trap detectors are used as transfer standards of optical power at visible wavelengths because they have a predictable spectral responsivity. New results on transmittance measurements of PRC Krochmann V(λ) filters are presented, especially the angle and temperature dependence of the transmittance. The characterized trap detector and the V(λ) filter are used for a novel realization of the SI base unit of luminous intensity, the candela. Test measurements indicate a good agreement with previous photometric scales.