Realization of the unit of luminous intensity at the HUT

A description is presented of an upgraded trap-detector-based realization o f the units of luminous intensity (candela) and illuminance (lux) at the He lsinki University of Technology (HUT). The realization is accomplished usin g a reference photometer, a light source and a distance-measurement system. A thorough characterization is presented of the reference photometer, cons isting of a reflection trap detector, a temperature-controlled V(lambda) fi lter and a high-precision aperture. The maintenance of the units is describ ed. An updated uncertainty budget of the realization is given. Two of the t hree main uncertainty components of our earlier realizations have been sign ificantly decreased. The uncertainty analysis indicates a relative expanded uncertainty(1) of 2.2 x 10(-3) for the realization of the candela and 1.8 x 10(-3) for that of the lux. The HUT has participated in three internation al measurement comparisons, whose results are reviewed. According to the re sults, the HUT candela deviates by +4.0 x 10(-3) from the candela of the Sw edish National Testing and Research Institute with an expanded uncertainty of 10(-2), -2.7 x 10(-3) from that of the National Physical Laboratory (UK) with an expanded uncertainty of 5.6 x 10(-3), and -3.3 x 10(-3) from the w orld mean with an expanded uncertainty of 5.9 x 10(-3).