CRI

Color rendering index CRI

The index is a measurement of light in relation to how well the different colors of the illuminated object are reproduced by the light source. Basically, a CRI of 100 means that the colors are reproduced in the best possible way. A CRI of 0 means colors are not reproduced at all, so you see everything in black and white. Interior lighting should always have a Ra value (Ra is the unit of color rendering index) of over 80. All LIMENTE light fixtures have a CRI of over 80 and LUX models of up to 95.

Color rendering is evaluated using the CIE method. It is determined based on how the light source reflects off a set of eight color patches with respect to a reference light source. The light source tested and the reference light are both shined at the set of eight specific colors, and each color is given a score of 1-100. The Color Rendering Index (CRI) is the average of the scores.

Determining CRI

Color rendering index is determined by comparing the reproduction of 15 different colors in the light being tested to that in the reference light. These 15 different colors each correspond to a specific wavelength of color. See below for example on some measurements of a light fixture’s ability to reproduce different colors. Previously, only eight different colors were used to measure CRI and, for example, red was not included in the spectrum (R1, R2, R3, R4, R5, R6, R7 and R8).

The CIE (International Commission on Illumination) defines the references used.

Currently, two different light sources are used to measure the color rendering index, depending on the color temperature of the light source being measured. All LIMENTE light fixtures have a color temperature of 2700K-4200K and use Planck’s radiation (the black body spectrum) as reference.

The reference light source aims to mimic sunlight during the day without distortion.

Same CRI for two light fixtures - do colors reproduce in the same way?

Since only 15 colors are used to measure the color rendering index (CRI), it is possible that two light sources with the same CRI do not have the same ability to reproduce colors. The calculated index is based on arithmetic average, which means that some of the measured scores may be relatively poor, and yet the average is a reasonably good number. Hence, even with a same CRI, one light source may be significantly better than another.

Although, as a single value, CRI isn’t the only thing to consider when choosing lighting for your home, it’s always best to choose lighting with a higher CRI rating so you can be sure the color portrayal in your home is most accurate. This is why you’ll find light fixtures with extremely high (CRI>95) values in our LIMENTE LUX collection!

The colors below are used for determining CRI.

Determing CRI becomes more accurate in the future

Ever since LEDs, there’s been a need for a new type of a metric that measures for the best possible light. The International Commission on Illumination, CIE, is currently working on a new, more precise method for determining the color rendering index. Please see the figure below for an example of what the measured values of different wavelengths (colors) could be. Presumably, color rendition will use 99 color samples instead of the current 8 in the future, which makes it almost perfectly matched to the color rendition the human eye is able to detect.

Follow the link below to read more about the CIE’s publications and activities:

CIE - International Comission of Illumination