Uncertainty budget for PTB’s gonioreflectometers and ways to improve it in the short VIS spectral range

Abstract

This paper describes a detailed derivation of the uncertainty budget for measurements of the absolute spectral radiance factor with PTB’s gonioreflectometers. The measurement uncertainty is determined according to the ‘Guide to the expression of uncertainty in measurement’ provided by the Bureau International des Poids et Mesures. To give an insight, the uncertainty analysis is applied to measurements of three ceramic samples. The influence of different systematic and statistical sources of uncertainty and their contributions are discussed in detail. For wavelengths larger than 450 nm the total measurement uncertainty is dominated by systematic contributions. Towards UVA the major contribution is caused by statistical effects, which are mainly due to the decreasing power of the radiation source used. We present an approach capable to reduce this contribution for the VIS/UVA-transition spectral range by means of a specially designed LED-based sphere radiation source.