This section specifies a method for determining the relative lighting power of white pigments by adding a carbon black pigment formulation to a plasticized polyvinyl chloride (PVC) (PVC-P) base mixture of a certain white pigment content. Applicable to the determination of the relative lighting power of white pigments. Terms and definitions include lighting power and relative lighting power, the latter indicating the ratio of the sample lighting power to the agreed reference pigment lighting power, expressed as a percentage. Test instruments and materials include a two-roll machine, a tablet press, and a photometer, in which the two-roll machine needs to have the characteristics of heating and adjustable spacing of the two rolls. Rollers with chrome-plated surfaces are preferred.