Defined by spectrum locus
Path Length: Depends on saturation of sample colour.
A Colour space in which values L*, a* and b* are plotted using a Cartesian coordinate system. Equal distances in the space approximately represent equal colour differences. L* represents lightness; a* represents the red/green axis; and b* represents the yellow/blue axis. CIE L*a*b* is a popular colour space for measuring both reflective and transmissive samples.