The situation with the metrological assurance of brightness measurements in Ukraine is analyzed. The main regulatory documents for the characterization of lux meters are considered. It was noted, that the components of the uncertainty of brightness due to the difference in the spectral composition of radiation, during calibration and measurement, as well as uncertainties due to spatial heterogeneity of the screens, are not fully considered. The characteristic values of these uncertainties are calculated by the method of mathematical modeling, using generally accepted calculation methods. To calculate the spectral errors, the literature data on the spectra of CCFL and LED monitors were used, as well as the modeling of the spectra of blue, green and red radiation sources, using Gaussian distribution with varying widths. It is shown, that for а brightness meter calibrated by а type A source, the use of white screens for measuring the brightness will result in errors, less than 7%. It is shown, that when calibrating the brightness meter using the CCFL screen and then using the LED for the screen, the errors will be about 1%. Simple formulas are given to evaluate the effect of screen heterogeneity. For а refined assessment of the influence of spatial inhomogeneity, mathematical modeling was carried out — 3 types of brightness distribution, were used with decreasing radiation distribution density and two types of viewing area — а circle (imitation of brightness measurement, using а diaphragm) and а Gaussian distribution (imitation of brightness measurement with а lens) equal widths. It is shown, that for the field of sight in the form of а Gaussian distribution, the influence of the inhomogeneity of the distribution of screen illumination, when moving and changing the width of the field of sight is insignificant. Two approaches have been proposed for building the material base for metrological assurance of brightness measurements.
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