Chromatic/color reproduction vs CRI
The concept of chromatic, or color, reproduction, refers to the way in which objects appear when they are lighted by a light source. In order to assess the quality of the result, there are at least three main aspects that we should take into account:
Accuracy: The ability that a light source has to faithfully reproduce the colors, compared to a light source that we take as a reference (or consider ideal).
Vividness: The ability that a light source has to represent the colors so objects appear in a vivid way.
Discrimination: The ability that a light source has to allow the viewer to tell apart a great variety of colors when they are presented simultaneously.
The relative significance that each of them will have will depend on the application.
Due to the need to establish procedures that allow to numerically assess the chromatic reproduction, there are several methods that have been historically developed, all of them useful but far from perfect. These deficiencies turned especially relevant with the emergence of LEDs, because their spectral distributions are considerably different from those of the light sources that served as a basis to establish the different procedures.
Among these methods, some are based on the comparison with a reference light source; others are based on the width of the reproduced color palette; there are even some others that develop by dividing the visible spectrum into bands. However, for the time being, only one of them, the CRI —Color Reproduction Index—, is widely applied and has been approved by the International Lighting Commission (ILC).
The CRI is an accuracy measure —how real are colors seen when compared with a reference source— but doesn’t take into account the other two aspects: intensity and discrimination. That is why it isn’t a contradiction that, for some uses, light sources with relatively low CRI are able to offer color results considerably better than others with a superior value.
Thus, it is important to emphasize that chromatic/color reproduction and CRI have different meanings. The first refers to a wide concept related to the —subjective—perception of color. The second is a numerical value that we get with the aim to assess the first, by using a standard procedure; i. e., objective.
In the next post we will see with greater detail how CRI is calculated and which are its main constraints, beyond the ones already mentioned.