The historical milestones in the search for uniform brightness and lightness scales are described in Wyszecki and Stiles [12, pp. 493-499]. Typical experiments determine these scales either by a process of repeated bisection of the scale extremes or by moving up in increments of a JND. A cube-root power law relation between brightness and luminance provides a satisfactory fit for most experimental **data** and, therefore, has the most widespread acceptance at present [12, p. 494].