What is CIELUV color space?

  Reference: http://dcssrv1.oit.uci.edu/~wiedeman/cspace/me/infoluv.html

  The CIE, which stands for Commision Internationale de I'Eclairage (or International Commission on Illumination), in 1931, defined three standard primaries (X, Y, and Z) to replace red, green, and blue. It is inevitable since all visible colors could not be specified with only positive of red, green , and blue components. With this newly created X,Y, and Z primaries, all visible colors can be specified with only positive values of the primaries. Following picture shows the cone of visible colors, as well as the plane X+Y+Z=1. 

  Lowercase x,y, and z refer to the normalized X,Y and Z such that x = X/(X+Y+Z), y = Y/(X+Y+Z), and z = Z/(X+Y+Z). These lowercase letters are called chromaticity value. and a projection onto the (X,Y) plane of the (X+Y+Z = 1) plane of the above figure is called chromaticity diagram which is shown to following picture. The numbers along the boundary correspond to wavelength in nanometers.  

 The CIE LUV color space is a perceptually uniform derivation of this standard CIE XYZ space. Perceptually uniform means that two colors that are equally distant in the color space are equally distant perceptually). In this color space, the distance between two colors tells how different the colors are in luminance, chroma, and hue.