State primary standard for units of luminous intensity and luminous flux GET 5-2024

The history of the modernization of the national standard for the unit of luminous intensity in Russia is presented: from the establishment of the first state light standard in 1925 at Main Chamber of Weights and Measures (today – the D. I. Mendeleev Institute for Metrology) under the leadership of P. I. Tikhodeev to its current version – the State primary standard for units of luminous intensity and luminous fl ux GET 5-2024. As a result of the latest modernization, the GET 5-2024 now includes newly developed and manufactured by All-Russian Research Institute for Optical and Physical Measurements standard facilities, based on the latest research findings. For the first time in global practice, the unit of luminous intensity – the candela – is reproduced in GET 5-2024 using a high-temperature blackbody model operating at a fixed thermodynamic temperature of 2856.67 K, corresponding to the phase transition melting point of the molybdenum-carbon compound δ(MoC)-C. This approach has enabled an expanded uncertainty in the reproduction of the candela not exceeding 0.2 % at the level of 388.52 cd (with a coverage factor 2). Additionally, the use of a variable-temperature blackbody model allows for the reproduction of luminous intensity in the range from 1 to 20000 cd, with an expanded uncertainty not exceeding 0.24 % (with a coverage factor 2). The unit of total luminous fl ux – the lumen – is reproduced using a goniometric method with a specially developed goniophotometer. The reproduction range for luminous fl ux is from 1 to 3500 lm, with an expanded uncertainty of 0.22–0.28 % (with a coverage factor 2). Thus, the modernization of GET 5-2024 has extended the reproduction ranges of the units of luminous intensity and luminous fl ux and improved the accuracy of their realization. The improved GET 5-2024 allows the reproduction of the unit of luminous intensity in accordance with the recommendations of the International Committee of Weights and Measures, which ensures international compatibility of the results of scientific and applied measurements, their accuracy, and also contributes to improving the quality of industrial products, increasing transport safety, etc.

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