An account is given of the Television Consistency Index method of assessing the colorimetric properties of light sources for use in television scene lighting. Theoretical limits have been determined within which this Index may be used as a general description of lamp performance, bearing in mind the inevitable differences in spectral analysis characteristics (spectral sensitivities) which exist between one practical colour television camera and another. Practical comparisons between displayed colour telvision scenes are described, in which the original scenes were illuminated by different lamps. The results of these tests are used to examine the validity of the Television Consistency Index, both in absolute terms and in relation to the alternative use of the General Colour Rendering Index in this context.