Calibration of Reflectance Standards.

Measurements of the diffuse spectral reflectance are usually not made as direct measurement of the incident and the reflected radiant flux but rather as measurements relative to a standard of known reflectance value. For the calibration of such standards, different methods have been described in the literature: Goniophotometric methods, also called Indicatrix methods or point-by-point methods.Methods based on the Kubelka-Munk theory.Integrating sphere methods according to Taylor, Benford, Sharp-Little, van den Akker, Korte. Various materials such as magnesium oxide, barium sulfate or opal glass are being used as standards. Their suitability as transfer or as working standards will be discussed. The results of comparative measurements between some of these methods will be given.