In the field of goniophotometry, as in many other measurement disciplines, there is an increasing need for laboratories to become ISO-17025 accredited. This involves, amongst other things, characterisation of the goniophotometric measurement for uncertainty analysis and laboratory intercomparisons. Simple comparison of the luminous intensity measurements, however, can lead to large errors where there is a steep luminous intensity gradient when the only difference between the two sets of measurements is a small discrepancy in alignment. Given the difficulty in mounting and aligning some types of luminaires, this makes uncertainty analysis and intercomparisons difficult. Furthermore, the work of several CIE Division 2 Technical Committees (e.g. TC2-62) highlights the need to compare the measurements made on both far-field and near-field goniophotometers. This paper introduces a metric for comparison of two luminous intensity distributions that isolates and removes discrepancies that arise both from misalignment and also the difference in absolute calibration scales or the luminous flux output of the source. Moreover, these discrepancies are reported as part of the metric, so that a complete comparison of the sets of measurements is possible.

One of the key parameters in the photometry of solid-state lighting is the measurement of the luminous efficacy of the device under test. This parameter requires not only accurate photometric measurements, but also accurate measurement of the electrical parameters of the device. It has become apparent that high-accuracy electrical measurements of lighting devices and solid-state lighting devices, in particular, are subject to much greater errors when the current waveform departs from a pure sinusoidal waveform. Key aspects influencing this are the calibration of the power analyser used for the measurement and the wiring arrangement used during the measurement. This paper describes a method of waveform-specific calibration for power analysers, and a simple, common error used in the wiring setup, which can result in significant errors.

This paper presents a comparison of measurements of the waveforms of temporal light modulation (TLM) from eight light sources performed by two different laboratories. The study focuses on the methodology of extracting relevant numerical differences between the measured waveforms. The methodology involves frequency matching, duration matching, selection of sampling interval, phase matching, and normalization. Results of the use of the methodology are presented. The results show that for some waveforms the comparison method can be used to practically explore equivalency of measurements.

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