Correlated colour temperature - uncertainty and estimation

Correlated colour temperature (CCT) of a source is estimated from position in CIE 1960 ( u , v ) colour space in relation to the black-body locus. In this paper, the methods of the ISO Guide to the Expression of Uncertainty in Measurement are applied to derive analytical expressions for uncertainty in u and v chromacity coordinates and CCT, including correlation effects. Uncertainty in CCT is found by fitting the form of the black-body locus and relevant derivatives. Examples are given for calibration of four typical sources of spectral distributions. Accurate CCT is determined by a search technique. An alternative method using fitted functions to solve for CCT using the geometry in ( u , v ) space is presented. An uncertainty in CCT of a few kelvin can be achieved.