A review of colour rendering indices and their application to commercial light sources

The CIE colour rendering index (R_a) is the most widely used measure for quantifying and comparing the colour rendering performance of light sources. Despite its prominence R_a is not without limitations, including its reliance on reference standards and the inability to compare the R_a of sources with different correlated colour temperatures. Other colour rendering measures have been proposed including several based on colour preference, others based on absolute scales, and some that are graphical rather than numerical. This paper utilizes nine colour rendering indices to assess and compare the performance of common light sources and theoretical illuminants. Following this assessment, recommendations for the use of existing tools are made, as well as suggested strategies for future colour rendering measures.