This International Standard specifies a method for the determination of light absorption of cellulose acetate, employing test specimens taken from two mouldings which have been produced using different periods of heating. The aim is to provide quantitative measurements which are compatible with visual judgements of yellowness and lightness, and of changes in these properties after moulding. The determinations are carried out on cellulose acetate in plasticized form rather than in solution, since a more reliable guide is thereby obtained to the performance of cellulose acetate in plastics materials. This method minimizes the effects of haze or imperfections in the specimens. This method is intended for cellulose acetate having an acetic acid yield of 54 % ± 2,5 % . It may also be applicable to other transparent plastics which are not strongly coloured and which can be moulded under the specified conditions.