In 1942 Duntley published a paper giving a theory that describes the reflectance and transmittance of light-diffusing mats. This theory avoids the logical objections that apply to the two-constant theory developed by Kubelka and Munk, and other contributors. This paper describes new ways of determining the five coefficients that appear in Duntley’s theory. It discusses the characteristic features of light-scattering mats that follow this theory, emphasizing the points of difference with the two-constant theory. Results of laboratory measurements are given which demonstrate the utility of Duntley’s theory, and show the dangers of using the two-constant theory as a research tool.
ARTHUR L. LATHROP, "Diffuse Scattered Radiation Theories of Duntley and of Kubelka-Munk," J. Opt. Soc. Am. 55, 1097-1102 (1965)