While the human eye does not respond linearly to density and luminance changes, it does respond linearly to lightness L*. Equal increments on the L* scale do represent approximately equal steps in the perceived lightness of related colors. Near uniform color scales are available wherein equal differences...http://www.google.com.au/patents/US4949135?utm_source=gb-gplus-sharePatent US4949135 - Visual based process control apparatus which is based on a near uniform human visual response space
