what is the difference between CRI and CQS?

CRI and CQS Rainbow LightThe range of spectrometers available from Edaphic Scientific provide an output in the software for CRI and CQS. But what is CRI and CQS? And what is the difference between them?

CRI is an acronym for Colour Rendering Index, a scale or quantitative measure of the ability of a light source to reveal the actual or real colours of objects when compared with an ideal light source. CQS is an acronym for Colour Quality Scale and it’s an improved quantitative measure of colour quality than CRI which has been developed by National Institute of Standards and Technology (NIST).

CRI and CQS are particularly important indices for LED light sources, or solid state light (SSL) sources, where the quality of colour is critical. In industries such as photography and cinematography the CRI and CQS are important indices. The CRI and CQS are a quantitative, scientific, measure of the ability of an artificial LED light to reveal the real colours of an object.

The currently accepted international standard for determining the colour appearance of objects is the CRI. This index has been approved by the International Commission on Illumination (usually abbreviated CIE for its French name, Commission internationale de l’éclairage). However, the CRI is not perfect and many scientists agree that there are problems with the index. For example, the CRI is based on an outdated uniform colour space (1964 W*U*V) and an outdated correction parameter (the Von Kries chromatic adaptation correction). The CRI also penalizes LED lights whether they increase or decrease shifts in hue, chroma and lightness, even when an increase in these parameters is generally desirable. There are also technical issues with the CRI in reference to the CCT (correlated colour temperature).

The CQS is an updated index that has been designed to address the shortcomings of the CRI. The CQS is yet to be formally adopted by the CIE, however the National Institute of Standards and Technology (NIST), a US government institution within the Department of Commerce, is the main advocate of the CQS and is pushing for its adoption. Computational simulations and subjective evaluations of the CQS have shown that it does address the shortcomings of the CRI and possibly provides more robust information on the colour quality of a LED light. However, thorough scientific experimentation still needs to be performed on the CQS prior to its widespread adoption. NIST is currently undertaking these experiments at its spectrally tunable lighting facility.

Rainbow Light’s optical spectrometers provide an output for both the CRI and CQS. Therefore, the user can decide to adopt either or both indices in testing the quality of their LED light.