Relative Brightness

3.1 Contrast

 

Contrast (C) describes the difference in appearance of two parts of a visual field seen simultaneously or successively.

(2)

where Lt = luminance of the target, cd/m2

                Lb = luminance of the background, cd/m2

3.2 Contrast Rendering Factor

 

Contrast Rendering Factor (CRF) is the ratio of the detectable contrast in a task under a given lighting system (C1) to that under fully diffused reference lighting (C2).

(3)

The reference lighting conditions are completely diffuse and unpolarized illumination from a photometric integrating sphere where light comes equally from all direction.