The concept of correlated colour temperature revisited

Correlated colour temperature is a one-dimensional description of the colou r of near-white light sources. The concept relates the numerical value to a visual observation of smallest colour difference between the chromaticity, of the test source and of a point lying on the Planckian locus. In practic e, chromaticity difference on a uniform chromaticity scale diagram is used. Since the introduction of the CIELUV and CIELAB spaces, it has been questi oned whether the calculations should be done on the traditional u,v diagram , or by using a more equidistant colour space. Based on our visual experime nts, we can state that the u,v diagram-based calculation is adequate to des cribe the correlated colour temperature of a source. The individual scatter of observations is so large that a visual definition has no practical real ity. Thus, we recommend changing the definition of correlated colour temper ature from a visual definition to a mathematical one and dropping any refer ence to visual investigations. (C) 2001 John Wiley & Sons, Inc.