In 1931 the International Lighting Commission (CIE - Commission Internationale de l'Eclairage) initiated a uniform system for describing colors of light.
The
CIE
system is based on the sense of vision and on physical data, and relates only to hue and saturation.
The graphic description of the
CIE
system is based on a triangular iron-shaped form. Surrounding the triangle are the values of the wavelengths of pure color (1) . On the straight line which connects the vertices of the triangle between 400 and 700 nm are colors which do not exist in the continuous spectrum. These are hues of magenta which can be produced by mixing red and blue (two vertices of the triangle). The center of the triangle, marked E is where all of the hues are juxtaposed, producing white light.
Certain areas in the
CIE
diagram, in particular the area between 400 and 560 (blue to green) are larger than the areas of yellow to red. This is a function of the shape of the visual sensitivity curve, which is based on the research of human visual sensitivity.
The part of the
spectrum
surrounding 555 nm (yellow) is experienced as being the brightest zone; visual ability decreases sharply at each corner of the triangle: at the red end of the
spectrum
in the range between 600-720 nm, and at the blue end of the
spectrum
in the range between 400-480 nm. The
CIE
system proposes an objective standard for designating the color of light,
independent
of the illuminated object, of absorbing or reflective surfaces, and of the pigment makeup. The
CIE
system is based purely on
wavelength
measurements and makes it possible to designate, using the X and Y coordinates , any hue by calculating the relationship between the different wavelengths of which it is comprised. Any color can be described simply by locating it on the coordinates of the diagram. The
CIE
established four standards of illumination: a tungsten
lamp
at 2856OK, and three states of daylight: 4870OK, 6770OK and 6500OK. see more
