This Part of EN 13523 defines terms of the procedure for determining the metamerism of a colour match of an organic coating on a metallic substrate.
When two colour specimens have identical spectral reflection curves, they are matching under any illuminant irrespective of its spectral characteristics. This is termed a "spectral match". It is also possible for two colour specimens having different spectral reflection curves to match visually under a given light source but not to match under another light source with different spectral characteristics; such matches are termed "metameric".
One quantitative description of metamerism is the so-called "metamerism index".
The information of the metamerism index is of limited value where E (instrumental colour difference for a given illuminant, see EN 13523-3:2001) is > 0,5. The metamerism index is not suited for determining the absolute colour difference or colour constancy of a given specimen at change of illuminant.
The colour difference under the reference illuminant is to be measured in colour coordinates L*, a* and b* (see EN 13523-3:2001).
Excluded from this method are organic coatings producing fluorescence and/or which are multicoloured, pearlescent or metallic.