On the uncertainties of photometric data for luminaires

Abstract

This paper describes an investigation of the magnitude of uncertainties which can be expected on the photometric data for commercially available luminaires. Ten manufacturers and importers of luminaires in Sweden and Denmark have taken part in the investigation. Fifty-six luminaires have been selected by personnel from the Danish Illuminating Laboratory from the storerooms of these manufacturers and importers and measured at the laboratory. The measurements have been compared to the data, which the manufacturers have published in their catalogues. The comparisons have included light output ratios of the luminaires, coefficients of utilisation and BZ-classifications. Furthermore, the shape of the light distributions as well as the degree of asymmetry have been included. In order to evaluate the differences in these properties two new quantities: 'difference index' and 'asymmetry index' have been proposed. The conclusion of the investigation is that for scarcely half of the luminaires the catalogue data are satisfactory. However, a few of the luminaires show quite unacceptably great discrepancies. The causes of these discrepancies have not been investigated.