CIE x048-WP03

The general V(A) mismatch index, f_1^' quantifies the mismatch between the spectral responsivity of a photometer, s(A), and the spectral luminous efficiency function, V(A). A short review of its historical development is given to explain the reasons for the current definition and which adjustments may be useful for the future. The properties of the current definition are described in detail.
It is very likely that in the future, calibration of photometers will be done with a white LED light source as reference. It might involve the need for a more adequate definition of the general V(A) mismatch index, either by using a different normalization in f_1^' for the spectral responsivity of the photometer or by introducing a different type of function for assessing the mismatch. On the other hand, the measurement of coloured LEDs is also becoming increasingly important. Is a single quality index for white and coloured light sources sufficient?