When choose a light for photography or home lighting, we will see a term CRI (Color rendering index).
An object appears some color, for example red, it is because it reflects red wavelengths, but absorbs others. However, not all white light sources provide same amount of color wavelength light.
CRI is a value indicates that a light source will make objects appear very similar to how they would look under natural lighting conditions. The maximum possible score of CRI is 100. A CRI score of 95 or above is considered very high.
There are sub-scores of CRI known as “R" values, for example, R1-R15. Each R value represents the light source’s color rendering ability for a particular color. The average of R1-R8 values is called CRI Ra, when people talk about CRI, we usually refer to the CRI ra value. However, other R values are also important, such as R9. CRI R9 is a very important metric because many light sources will be lacking in red content, this will make red colors appear to be faded. Red is a crucial color for many applications including photography, textiles and reproduction of human skin tones.