Requirements for reflection standards and the measurement of their reflection values.

The standards necessary for transferring the reflection scale must meet certain requirements. First, the present paper discusses the question of how far these requirements are met by the materials now used for realizing the reflection standards. Then the instrumentation is described that was developed in the Physikalisch-Technische Bundesanstalt for measuring the spectral radiance factor beta(lambda) for the d/O and 45/0 geometries and in principle also for the inverse geometries. How these measurements are made so that the values obtained for a material standard are related to the perfect reflecting diffuser as the primary standard is discussed.