This part of ISO 787 describes a general method of test for comparing the resistance to light of samples of similar types of coloured pigments (agreed reference pigment and test sample). Two methods of exposure are described. In method A, the material is exposed under glass to natural light. In method B, the material is exposed to direct artificial light. NOTE - When either of these general methods (A or B) is applicable to a given pigment, only a cross-reference to the appropriate method should be included in the International Standard relating to that pigment, indicating any detailed modification that may be needed in view of the special properties of the product. Only when the procedures given in this general method are not applicable to a particular product should a different method for comparison of resistance to light be specified.