CIE 177

This Technical Report reviews the applicability of the CIE colour rendering index to white LED light sources based on the results of visual experiments. The currently recommended colour rendering index (CRI) calculation method was officially introduced in 1974, and is described in the current publication CIE 13.3-1995 (CIE, 1995). Visual experience has shown that the current CRI based ranking of a set of light sources containing white LED light sources contradicts the visual ranking. In this Technical Report, three recent visual experiments (including simulations) on colour rendering including white LED light sources are described that confirm this contradiction. It was concluded from these visual colour rendering results that the current CRI method did not describe well those situations where white LED light sources were involved i.e. if white LED light sources were visually ranked together with other light sources. Low correlation was found between the visual colour differences and the computed colour differences if the current CRI method was applied to calculate those colour differences. The conclusion of the Technical Committee is that the CIE CRI is generally not applicable to predict the colour rendering rank order of a set of light sources when white LED light sources are involved in this set. The Committee recommends the development of a new colour rendering index (or a set of new colour rendering indices) by a Division 1 Technical Committee. This index (or these indices) shall not replace the current CIE colour rendering index immediately. The usage of the new index or indices should provide information supplementary to the current CIE CRI, and replacement of CRI will be considered after successful integration of the new index. The new supplementary colour rendering index (or set of supplementary colour rendering indices) should be applicable to all types of light sources and not only to white LED light sources. Possibilities for an improved description of colour rendering are summarized in the Appendix of this Technical Report.