A generalized method of predicting photometric error sources due to the light emitting properties of the light source to be measured, is proposed. This method is based on a comparison of the radiant energy distributions of both test and standard sources on each axis in the space that characterizes the light emitting properties. As a result of applying this method to luminance measurement of color TV picture tubes, the following are determined to be error sources: (1) unusual spectral power distribution, (2) non-uniform luminance distribution over a phosphor screen, (3) deviation from the perfect diffusion, and (4) pulsed light due to electron beam scanning. Quantitative error analysis for a typical measurement shows that photometric errors due to the above sources are 2.6%, 0.1%, 1% and 2%, respectively.