This document specifies a substitution measurement method to measure internal quantum efficiency, external quantum efficiency and absorptance of ceramic phosphor powders, which are used in white light-emitting diodes (LEDs) and emit visible light when excited by UV or blue light. In this method, commercially available measurement equipment, such as a fluorescence spectrophotometer or a spectroradiometer equipped with a monochromatic light source as incident light, are used to measure fluorescence spectra for reference materials whose quantum efficiencies and absorptance have been determined using the methods in ISO 23946 and a phosphor material under test.