1.1 This practice provides a way of specifying the angular and spatial conditions of measurement and angular selectivity of a method of measuring the spectral reflectance factors of opaque gonioapparent materials, for a small number of sets of geometric conditions. 1.2 Measurements to characterize the appearance of retroreflective materials are of such a special nature that they are treated in other ASTM documents and are not included in the scope of this s