Colour Rendering - Explained Colour rendition is a crucial but often misunderstood aspect of any lighting installation. There are a few methods of measuring colour rendering, including TM-30, the Colour Quality Scale (CQS) and others, but this article will focus on the Colour Rendering Index (CRI) as this venerable system is still by far the most commonly used. What is colour rendering? Put simply, colour rendering is a measure of how accurate the colour of objects illuminated appears to be, when compared to a reference source. Things illuminated with a high CRI light source can be expected to look very similar to how they would in daylight, for example. What colour rendering doesn’t do is tell you anything about the colour of a light source; that’s instead determined by the colour temperature (CCT). It also doesn’t tell you the range of colours that can be seen under the light source- something known as the gamut area. How does CRI work? CRI is based on a set