Color rendering index (CRI) is the widely used criteria to evaluate the color rendition ability of light. Regarding the general CRI (Ra), it is the average of 8 values related to 8 test color samples, so-called TCS. There are also 7 test color samples more in extended CRI (Re) value calculation. To know more about the difference, please refer to “What is the difference between CRI, Ra, and Re?”.
What is Test Color Samples?
Since 1965, the CIE announced the method of Color Rendering Index calculation, based on 14 color samples, which is called Test Color Samples (TCS).
TCS(CIE) is the samples that describe the hue circle, which are moderate in saturation and almost the same in brightness. The first 8 samples are involved in general CRI (Ra) calculation, and other 6 color samples representing saturated blue, red, green and yellow, etc. are involved in extended CRI (Ra) calculation.