A correlated color temperature for illuminants

As has long been known, most of the artificial and natural illuminants do not match exactly any one of the Planckian colors.Therefore, strictly speaking, they can not be assigned a color temperature.A color of this type may, however, be correlated with a representative Planckian color.The method of determining correlated color temperature described in this paper consists in comparing the relative luminosities of each of the three primary red, green, and blue components of the source with similar values for the Planckian series.With such a comparison three component temperatures are obtained; that is, the red component of the source corresponds with that of the Planckian radiator at one temperature, its green component with that of the Planckian radiator at a second temperature, and its blue component with that of the Planckian radiator at a third temperature.The average of these three component temperatures is designated as the correlated color temperature of the source.The mean devia- tion of the component temperatures from the average temperature is used as a basis for specifying the color (chromaticity) departure of the source from that of the Planckian radiator at the correlated color temperature.The conjunctive wave length indicates the kind of color departure. CONTENTSPage I. Introduction 659 II.The proposed method 662 III.Procedure 665 1.The Planckian radiator evaluated in terms of relative lumi- nosity of the primary components 665 2. Computation of the correlated color temperature 670 3. Calculation of color departure in terms of sensation steps 672 4. Determination of the conjunctive wave length 674 IV.Characteristics of correlated color temperatures 674 1 .Color departure and the isotemperature line 674 2. Conjunctive wave length as a function of correlated color temperature 677 V. Correlated color temperature data for Davis-Gibson filters 2,450°t o 3,500°K.and 2,450°to 6,500°K 678 VI.