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The connection between illuminance and luminance measurements is considered to create a traceability link among a highly accurate illuminance meter, which is considered as an internal standard of the Photometric Laboratory, University of Padova, Padova, Italy, and other illuminance meters or photometric heads and luminance meters. After an introduction on themain involved definitions and equations linking the illuminance and the luminance measurements, this paper presents the instruments to which the procedures are applied and, at the end, results regarding the absolute calibration of the instruments under test, the check of their linearity, and the analysis of their spectral responsivity within the visible range. Following this way, this paper shows the main results in the connection among instruments devoted specifically to illuminance and luminance measurements. Then, it also introduces a comparison to other photometric heads, e.g., sensors that are part of more complex systems, like an integrating sphere for luminous flux measurement. In this last case, it has no significance to evaluate the difference between the absolute outputs, but it is interesting to compare the response of the two devices considering their linearity and their relative spectral response. A special section devoted to the evaluation of the spectral response presents a new simple but effective method. The application of a detector-based method allows a significant reduction of the uncertainty in the internal calibration of the photometric instruments, granting the continuity of the Photometric Laboratory operation contemporarily. [ABSTRACT FROM AUTHOR]

An accurate goniometer was constructed, being a part of a system that is designed for the measurement of reflecting properties of surfaces. It can be used to orient a surface of the sample under test arbitrarily with respect to the observing direction and the direction of the shooting light beam. The high performance (revolution angle uncertainty equal to 0.1°), which is required as a specification for the construction, is checked. Particular attention has been given to analyzing the orthogonality among the revolution axes of each goniometer component and their convergence in the goniometer center. The linearity error of each revolution motion has been measured by using a differential method, which proves to be effective in highlighting the small linearity deviation and verifying the uncertainty declared by the manufacturer. [ABSTRACT FROM AUTHOR]