Tristimulus values are spectrum integrals, involving a test light, that predict the quantities of three primary lights that when mixed together will match the test light. As described widely elsewhere, tristimulus values depend on the selected primary lights. However, tristimulus values are invariant to change of the integrand's domain (e.g., from wavelength to frequency), and also to change of range (e.g., from quanta to energy units). Starting with that invariance, this tutorial note explains how to transform the factors in the tristimulus-value integrand so as to obtain consistency among these representations of the tristimulus value. (C) 2016 Wiley Periodicals, Inc.