This test is especially valuable with tinted whites and coatings containing organic dyes. It is normally carried out by exposing part of the coated panel to a carbon arc in a rotating drum and comparing the exposed and unexposed parts for colour changes at fixed intervals. Accurate correlation between the arc and natural sunlight exposure is not possible.

The carbon arc is used for testing because results are consistent while the varying power of the sunlight makes outdoor exposures difficult to standardise. Nevertheless, it is advisable to confirm by outdoor exposure that the order of fading, as assessed by the arc test, is reasonable comparable with that obtained from tests under natural sunlight.