The R9 color rendering value is a specific component of the Color Rendering Index (CRI). The CRI measures a light source’s ability to accurately reproduce the colors of objects compared to a reference light source. While the CRI takes into account the average values of R1 to R8, the R9 value specifically focuses on the light source’s ability to accurately render the color red. The R9 value is not included in the overall calculation of the CRI. This means that even if a light source has a high CRI, it may not necessarily have a high R9 value, indicating a potential deficiency in accurately rendering red colors.