The CRI or color rendering index

The color rendering index(CRI) is a numerical value that summarizes the ability of a light source, such as an LED ceiling light, to render colors compared to natural light (CRI=100). This measure takes into account the response of the human eye.

How CRI is calculated

The CRI value of a light source is calculated by comparing the appearance of a given color sample with that of the same range of colors under natural light or a standardized light of the same color temperature that serves as a reference. For color temperatures up to 5000K a black body is used and for higher temperatures daylight is used. With the results of each sample an arithmetic average is made that will define the global capacity of our source to reproduce the colors without distorting them.

NameAppearance under sunlightColour
TCS01R1Light greenish red
TCS02R2Dark greyish yellow
TCS03R3Intense yellowish green
TCS04R4Light yellowish green
TCS05R5Light bluish green
TCS06R6Light blue
TCS07R7Light violet
TCS08R8Light reddish lilac

If there is something we must keep in mind is that the color rendering index is an average of the performance of the light source from a strictly colorimetric point of view and does not take into account the spectrum of the emitted light. This means that two bulbs with the same CRI value may not represent the colors of objects in the same way, especially if they are from different manufacturers.

Usefulness of the color rendering index

The main advantage of knowing this measure is to be able to quantitatively evaluate the quality of a bulb and compare it with others. In general, we will look for the CRI of our light source to be at least 80. However, in specific applications, such as stores or showrooms, it is advisable to use values that are even higher than 90, such as the Alabama series pendant lamps.

Different CRIs

Other indices for measuring the quality of light

The CRI, although the most widespread, is not the only method available to evaluate how a light source represents colors. Currently, we can highlight above all the CQS and the TLCi, which we will explain below:

Color Quality Scale (CQS)

Developed by NIST (National Institute of Standards and Technology) to compensate for some of the problems of the CRI, in fact it is a modification of it. This system uses more saturated color samples and uses the root mean square value of the samples instead of the arithmetic mean.

TLCI (Television Lighting Consistency Index)

This replaces the response of the human eye with that of a camera and uses a wider sample of colors. TLCI also ranges up to 100 and indicates whether color correction of the footage will be necessary.

85 – 100No need
70 – 85Simple
50 – 70Complex
25 – 50Complex. Will still not look good
<25Impossible to correct

In summary, the color rendering index of a light source will tell us how well it reproduces the colors of objects. The higher this value, the more natural the colors displayed will appear.