CIE Position Statement on Color Quality Metrics
The color perception of object colors has been an ongoing topic for a very long amount of time. This motivated scientists from all over the world to find a theoretical description of color rendering. This culminated in 1965 in the CIE's publication of the General Color Rendering Index Ra. The index has since then been accepted widely and been broadly applied in both scientific and industrial applications.
However, the CIE General Color Rendering Index Ra is not perfect. This became especially apparent with the rise of LED based light sources and luminaires. In many, cases the narrowband characteristics of LEDs led to a significant mismatch of the calculated Ra values and actual color rendering perception through humans. Hence, work on color rendering metrics was continued. This led to the publication of the CIE General Color Fidelity Index Rf in CIE 224:2017 [1]. This new index is based on 99 test color samples. Their distribution is optimized on capturing color rendering properties of LEDs and other sources to a much finer degree than is possible via the General Color Rendering Index Ra (based on only 14 test color samples).
Since 2017, the Color Fidelity Index Rf has been widely applied and a good agreement with human color rendering perception has been confirmed. Hence, CIE decided to recommend using the General Color Fidelity Index Rf not only in scientific but also in industrial application by the whole lighting community [2]. The aim is to replace the Color Rendering Index in the near future. The transition to the new metric should be alleviated by reporting both the old General Color Rendering Index Ra alongside the new General Color Fidelity Index Rf.
Gigahertz-Optik has introduced the CIE General Color Rendering Fidelity Index Rf alongside the Color Gamut Index Rg into all of its current spectroradiometers [3]. Calculating and displaying those values is supported by all devices of the BTS256 and BTS2048 series with sensitivity range from 360 nm to 830 nm or beyond. In addition, the measuring devices MSC15, CSS-45 and LIGHTmetric One offer Rf and Rg as measurands as well. Furthermore, in order to support current CIE recommendations all of those devices still display the classic CIE General Color Rendering Index Ra.
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