Brightness (also called effulgence) is an attribute of visual perception in which a source appears to emit a given amount of light. In Psychology, visual perception is the ability to interpret information from Visible light reaching the Eyes The resulting Perception is also Light, or visible light, is Electromagnetic radiation of a Wavelength that is visible to the Human eye (about 400–700 In other words, brightness is the perception elicited by the luminance of a visual target. Luminance is a photometric measure of the density of Luminous intensity in a given direction This is a subjective attribute/property of an object being observed. Property is any physical or virtual entity that is owned by an individual
"Brightness" was formerly used as a synonym for the photometric term luminance and (incorrectly) for the radiometric term radiance. This article deals with the usage of this term in Optics and Lighting. Luminance is a photometric measure of the density of Luminous intensity in a given direction In Optics, radiometry is the field that studies the Measurement of Electromagnetic radiation, including Visible light. Radiance and spectral radiance are radiometric measures that describe the amount of light that passes through or is emitted from a particular area and falls 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. Federal Standard 1037C, entitled Telecommunications Glossary of Telecommunication Terms is a United States Federal Standard issued by the General Services Administration 
A given target luminance can elicit different perceptions of brightness in different contexts; see, for example, White's illusion and Wertheimer-Benary illusion. White's illusion is an Optical illusion illustrating the fact that the same target Luminance can elicit different perceptions of Brightness in different Wertheimer is an Ashkenazi Jewish surname People with this surname include Alain & Gerard Wertheimer, French Jewish billionaires owners
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):
Brightness is also a color coordinate in the HSB or HSV color space (hue, saturation, and brightness or value). An RGB color space is any additive Color space based on the RGB color model. In Mathematics and Statistics, the arithmetic Mean (or simply the mean) of a list of numbers is the sum of all the members of the list divided HSL and HSV are two related representations of points in an RGB color space, which attempt to describe perceptual color relationships more accurately than In Colorimetry and Color theory, colorfulness, chroma, and saturation are related but distinct concepts referring to the perceived intensity
With regard to stars, brightness is quantified as apparent magnitude and absolute magnitude. A star is a massive luminous ball of plasma. The nearest star to Earth is the Sun, which is the source of most of the Energy on Earth The apparent magnitude ( m) of a celestial body is a measure of its Brightness as seen by an observer on Earth, normalized to the value In Astronomy, absolute magnitude (also known as absolute visual magnitude) is the Apparent magnitude an object would have if it were at a standard
The term "brightness" is also used in discussions of sound timbres, in a rough analogy with visual brightness. In Music, timbre (ˈtæm-bər' like timber, or, from Fr timbre tɛ̃bʁ is the quality of a Musical note or sound that distinguishes different Timbre researchers consider brightness to be one of the perceptually strongest distinctions between sounds, and formalize it acoustically as an indication of the amount of high-frequency content in a sound, using a measure such as the spectral centroid. The spectral centroid is a measure used in Digital signal processing to characterise an audio Spectrum.