The latest values for the constants of the black body are used, in conjunction with the Gibson-Tyndall luminous efficiency curve of the spectrum, to compute the luminous efficiency and brightness of the black body over a large range of temperatures. The value .00161 watts per lumen is used for the least mechanical equivalent of light. The computed values agree everywhere to within one per cent with the most recent experimental values.
HERBERT E. IVES, "The Luminous Properties Of The Black Body," J. Opt. Soc. Am. 12, 75-77 (1926)