Since light is defined quantitatively as radiant energy evaluated according to the CIE photopic luminosity curve, ordinary t units are inappropriate whenever the organism’s spectral sensitivity differs markedly from the CIE curve. Examples of differing spectral sensitivities include those of animals, of color defective individuals, and curves for all individuals under low light levels or with large fields. Calculations are presented of the amount of error involved when units of light are used for these inappropriate conditions; alternative solutions to the problem are discussed.
JoAnn S. Kinney, "Degree of Applicability and Consequences of Inappropriate Use of Units of Light," Appl. Opt. 6, 1473-1477 (1967)