International commission of lighting

See also: Co

The International commission of lighting (Co) (in English International Commission one Illumination ; in German Internationale Beleuchtungskommission ) is an international organization dedicated to the Lumière, the lighting, the Couleur, the spaces of color.

This commission was created to characterize the colors of the lights rationally such as the human brain sees them. With this intention it undertook systematic experiments of comparison of colors by many observers so as to define an average observer.

These experiments were interpreted within the framework of the physical definition of the lights like electromagnetic waves containing wavelengths ranging between roughly 400 and 700 nanometers (billionth of meters). This interval corresponds to the various colors of the rainbow between the purple one and the red or, more precisely, to the colors of decomposition of the white light by the prism. A wavelength thus characterizes a pure color (a color in the system TSL) while its luminous intensity characterizes its luminosity or value.

For the physicist, all new superposition of an unspecified number of pure colors defines a new color distinct from all the others. Our brain distinguishes the Couleur S through receivers called cones. It is that there exists in all and for all three types of cones, which means that color is characterized by three parameters, the intensities “measured” by the three cones or of the numbers which result some directly. It is noted that this system contains much less subjective colors than there are objective colors in physics (two indistinguishable colors for the human eye can be distinct for the apparatuses from physics). In addition, one can build a multitude of equivalent systems connected to each other by three equations.

The Co initially characterized in a precise way the natural system RVB which is based on the colors corresponding to the maximum of answer of each type of cones; to this end she asked the observers to adjust the intensities which it is necessary to give to the three colors so that their superposition reproduces a given color. This system is additive in accordance with the Lois of Grassmann according to which the characteristics of a light obtained by superimposing two lights are equal to the sums of the individual characteristics. Any other system deduced from this one by simple equations is also additive.

It is in particular the case of XYZ, developped at the point in 1931, which describes in a precise way the vision of the colors by eliminating certain defects from the RVB. The XYZ is transformed into xyY which replaces the decomposition in three primary educations by a decomposition in brightness and chrominance.

This last gave rise to a multitude of practical systems, whose L*a*b* which represents best the perception of the differences in colors but is not additive any more.

See too

the wikilivre of photography and more precisely the chapter dedicated to the photometry .
Not white

External bonds

http://www.cie.co.at/cie/ Official site of the Co
http://www.cie.co.at/framepublications.html lists publications and recommendations of the Co
http://www.efg2.com/Lab/index.html of others infos, many, on the color, the images,…

Category: Photometry Category: Colorimetry Category: Organization

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