CRI index levels for various lighting projects

The Color Rendering Index or CRI, for short, is a one number quantification of how good (or bad) is an artificial light source at reproducing colors, compared with reference standard illuminant modeled after daylight. The highest value possible is 100, equal with that of daylight and incandescent lamps/halogen lamps.  Other lamps, such as fluorescent or gas discharge lamps can have  CRI between 17 and 96, with even a negative value for sodium low pressure (the yellow type used in street lamps).

CRI was introduced by the International Commission on Illumination (CIE) in 1974, because of the wide variation in the ability to reproduce colors with the white light emitted by the many types of the gas-lamps mentioned above.

Today, with over 40 years of use, the CRI index is firmly rooted in the lighting industry and among professionals. However, it has failed to gain much traction among the general public due to the fact that, soon after its introduction, it became not really relevant when making a purchase decision for lighting.

The reason was that most lamps were built for specific applications that required a minim CRI value so one could not go wrong with the choice of lamp.

For example, for office or all other linear lighting almost everybody used the tri-phospor linear fluorescent tubes, on the market since the 70s, all with CRI over 80. For the home you the choice was between incandescent and halogen both with CRI100, for retail and other high intensity spot lighting the metal halide lamps with CRI min 85. Street light was reserved for high intensity and very efficient sodium lamps that although had poor CRI very few cared about it.

From 2000s onward, LED technology changed this. It is the first lighting source that can be used for every application and have the full range of performance and quality level, including the ability to accurately reproduce colors. Therefore, it is imperative you choose the LEDs with the correct CRI level for your application.

The pictures above shows how colors can look different based on the CRI of the light source that illuminates them. A vibrant red under sunlight or a high CRI light can look dull or even orange under a low CRI light.