Technology | Jul 28, 2010

Cnam Lounched Research Project on Characterization of Colour Rendering of LED Light Sources

The CIE method applied since 1974 for defining the CRI (colour rendering index) allows the quantification of the "quality" of the light generated by artificial light sources. This index ranging from 0 to 100 defines the capacity of a light source to reproduce the various colours of objects, compared to a reference source, but does not apply correctly to LEDs. So, new studies are recommended to determine a new colour index or indices which take white light produced by LEDs into account.

This task falls in the scope of the metrology of appearance. A new research project with the goal to work out a new method which would permit to quantify the colour rendering under different LED lighting, thanks to physical and visual measurements is established at LNE-INM/Cnam. Therefore a lot of different aspects will be considered.

The difficulty to measure what we see is to consider each elements intervening in the perception of an object: Lighting (of new sources like light emitting diodes), interactions of light with the material (with pearlescent or interferential facing), the reception of the light on the eye and its interpretation by the brain.

Determination of appearance requires the implementation of instruments and methods that will permit to measure the physical dimensions associated with sources (spectral power distribution) as well as with material characteristics (properties of reflection and transmission). These physical dimensions could be correlated to the human response obtained by visual measurements estimated for a group of persons in the form of a scientific modelling.

Spectral measurements will be made on the emission of samples thoroughly selected, illuminated by LED sources and by CIE reference sources to determine colour differences. These colour differences will be, then, compared with those obtained by visual measurements to look for a new colour rendering index.

Furthermore, metrological studies will be made on the characteristics of sources used and particularly on their luminance and their spectral power distribution stability, which seems not to be an unimportant parameter during the visual measurements. 

For information on the progress of the project please contact Nicolas Pousset (Optical radiation team, LNE-INM/Cnam, 61 Rue du Landy, 93210 La Plaine - Saint-Denis, France, e-mail: )