"Brightness" was formerly used as a synonym for the photometric term luminance and (incorrectly) for the radiometric term radiance. As defined by the US Federal Glossary of Telecommunication Terms (FS-1037C), "brightness" should now be used only for non-quantitative references to physiological sensations and perceptions of light.
In the RGB color space, brightness can be thought of as the arithmetic mean μ of the Red, Green, and Blue color coordinates (although some of the three components make the light seem brighter than others, which, again, may be compensated by some display systems automatically):
"Scanning System Having Brightness Compensation Apparatus and Method Thereof" in Patent Application Approval Process
Nov 29, 2012; By a News Reporter-Staff News Editor at Politics & Government Week -- A patent application by the inventors Tsai, Mi-lai (Keelung...