The entire diagram sits in Quadrant I of a
Cartesian Coordinate system, so that every color has its own X and Y
coordinates. However, the diagram is only two dimensional and lacks Brightness
information in the form of Luminous Transmittance or Luminous Reflectance.
A color is specified by giving its X and Y coordinates and a notation as to its
brightness.
Near the center of the diagram is the all
important Neutral Point. By extending a line from this point
through a color's X and Y coordinates out to the diagram's boundary, the color's
Dominant Wavelength can be determined. The distance along this line
from the neutral point to the color's position, expressed as a percentage of
the total length of this line, is the color's Excitation Purity.