Luminance contrast quantifies the relative brightness of an object against its background. It can range from zero to one. The closer the luminance contrast is to one, the greater the relative brightness of the object against its background.  Luminance contrast is a quantity defined by several different formulae, see the operational definition for details.
Original Source Chapter: Design Considerations. 

Provided By: LRC - National Lighting Product Information Program (NLPIP).  Operational definition by Peter Boyce.