The concept of correlated colour temperature revisited

Correlated colour temperature is a one‐dimensional description of the colour 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 practice, chromaticity difference on a uniform chromaticity scale diagram is used. Since the introduction of the CIELUV and CIELAB spaces, it has been questioned whether the calculations should be done on the traditional u , v diagram, or by using a more equidistant colour space. Based on our visual experiments, we can state that the u , v diagram‐based calculation is adequate to describe the correlated colour temperature of a source. The individual scatter of observations is so large that a visual definition has no practical reality. Thus, we recommend changing the definition of correlated colour temperature from a visual definition to a mathematical one and dropping any reference to visual investigations.