Use is made of the enormous inverse chromatic aberration of a zone plate to determine the dominant wave-length, so far as the eye is concerned, of the light from a lamp of definite color temperature transmitted through members of a group of gelatin filters. For representative members of the group this wave-length is compared with the center of gravity of the luminosity curve plotted with the aid of the energy distribution of the lamp, the transmission percentages for the filters and the visibility curve for the normal eye.
JOSEPH W. ELLIS and BARTHOLD W. SORGE, "Zone Plate Determination of Dominant Wave-Length of Filtered Lamp Light," J. Opt. Soc. Am. 24, 103-106 (1934)