Correlated color temperature as an explicit function of chromaticity coordinates

A simple equation to compute correlated color temperature (CCT) from CIE 1931 chromaticity coordinates x and y is given. Over the range of interest in color science, the errors are negligible. It was derived from the fact that the isotemperature lines for CCTs of principle interest nearly converge toward a point on the chromaticity diagram and the assumption that CCT may be represented by a third‐order polynomial function of the reciprocal of the slope of the line from that point to the chromaticity of the light. the equation is useful in designing sources to simulate CIE colorimetric illuminants.