Direct visual assessment of colour rendering

The colour-rendering index was introduced at the time when the second-generation fluorescent lamps (deluxe type) have been brought onto the market. At the time of developing the compact fluorescent lamp phosphors, they have been optimised to achieve good efficacy and high colour rendering index, and not good visual colour rendering. Today, a major technological breakthrough has led to a new generation of light sources based on LED technology. The emission spectra of these is different from that of fluorescent lamps, thus optimising these to achieve a high colour rendering index could again lead to differences between calculated and observed colour rendering. Before one can recommend a new mathematical model for calculating a colour-rendering index, one has to re-investigate the existing model and its usefulness. In the present work we describe some visual investigations and evaluate their correlation with the current method of colour rendering index calculation as well as with two possible updates of the calculation method. Also the question of updating the test samples gets consideration. Visual experiments have shown that the three investigated calculation methods, based on CIE Publ. 13.2, the CIELAB formula and a slightly modified CIECAM97s formula, differentiate only slightly, and to get to a proper colour rendering description the fundamental concept of determination has to be changed.