Commonly referred to as brightness, luminance is the proper term for the amount of light reflected or transmitted by an object.  A light-colored surface reflects more light than a dark one, therefore, more illumination is required on a dark surface to equal the luminance of a similar light surface.
 

Luminance is crucial for effective and quality vision.  For instance, a common experience would be the poor contrast between text and paper while trying to read the small print on a receipt. To increase luminance, we must take the receipt into better light in order intensify visibility.