Many specifiers base some of their requirements on the slight degradation in appearance of the parts tested, measured in terms of contrast.
The evaluation of the contrast is detailed and defined by international standard ISO 105 A02.
It involves comparing the degradation of the test piece using a grey scale, in a light booth in which the only illumination is standardised (type D65 Daylight).
This type of booth can also be used to inspect parts in other types of light, e.g. to check fluorescence phenomena.
This measurement is made by qualified technicians whose results are regularly compared with those obtained by the leading manufacturers.