The Colour Rendering Index (CRI) refers to the degree of how accurately a light source reproduces the actual colour of the object under illumination. The higher the CRI, the more accurately the light can display colours. The maximum value of the colour rendering index can go up to 100. 100 corresponds to the CRI of daylight and the natural light caused by sunlight.
Various types of light sources have different spectral distributions, thereby symbolising how broadly they cover the colour spectrum. Light Emitting Diode (LED) lights cover a high percentage of the colour spectrum, which is one of the reasons why they are considered superior to their incandescent and fluorescent counterparts.
Spectral distributions of different light sources across the visible spectrum
General and Special CRI classification for different colours
Through previous times, the CRI was considered as one of the pivotal parameters in validating the performance of different light sources across the lighting industry. However, the evolution of high quality LED Chip On Boards (COB’s) suggests the CRI will soon be considered outdated and a redundant method of analysing the lighting spectrum.
To overcome the limitations of CRI, the Colour Quality Scale was introduced as an index. The CQS integrates varied dimensions of colour quality, such as hue, lightness and saturation, which represents the overall colour quality of products for all types of light source. The CQS addresses the limitations of the CRI and substitutes the conventional two-dimensional approach with the latest, increasingly accurate three-dimensional one. This may suggest that a light source with a very high CRI value could rate substantially lower on the CQS scale.
Three-dimensional view of Colour Quality Scale
The following table indicates the comparisons that can be made between the CRI and the CQS:
Agreements to CRI
Deviations from CRI
Uniform object colour space to calculate colour differences
Different reflective samples
Reference source matched in CCT
Updated object colour space & chromatic adaptation transform
Single number output
The CQS is a contemporary measurement index that works for all types of light sources, having been tested through vision science experiments and simulations. The image below is a snapshot from a simulation that depicts a comparison between the reference trajectory with the observed trajectory for a light source. A 100 percent overlap of the two trajectories implies 100 percent colour quality for that light source. A larger deviation from the reference (indicated by the blue line) indicates a poorer colour quality.
Reference vs Test Simulation Trajectories for Colour Quality Performance
To find out more about the CRI and CQS indexes, Mondolux’s services or how we can help you find your best lighting solution, talk to us today.
Mondolux, Continually improving your lighting experience.