brightness

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Brightness is an attribute of
visual perception Visual perception is the ability to interpret the surrounding environment through photopic vision (daytime vision), color vision Color vision, a feature of visual perception, is an ability to perceive differences between light composed o ...
in which a source appears to be radiating or reflecting
light Light or visible light is electromagnetic radiation In physics Physics is the natural science that studies matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of ...
. In other words, brightness is the
perception Perception () is the organization, identification, and interpretation of sensory information in order to represent and understand the presented information or environment. All perception involves signals that go through the nervous system ...
elicited by the
luminance Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through, is emitted from, or is reflected from a particular area, and falls wit ...
of a visual target. The perception is not linear to luminance, and relies on the context of the viewing environment (for example, see White's illusion). Brightness is a subjective sensation of an object being observed and one of the color appearance parameters of many color appearance models, typically denoted as $Q$. Brightness refers to how much light ''appears to shine'' from something. This is a different perception than lightness, which is how light something appears ''compared to'' a similarly lit white object. The adjective '' bright'' derives from an Old English '' beorht'' with the same meaning via metathesis giving Middle English ''briht''. The word is from a
Common Germanic Proto-Germanic (abbreviated PGmc; also called Common Germanic) is the reconstructed proto-language of the Germanic branch of the Indo-European languages. Proto-Germanic eventually developed from pre-Proto-Germanic into three Germanic br ...
', ultimately from a PIE root with a closely related meaning, *' "white, bright". "Brightness" was formerly used as a synonym for the photometric term ''
luminance Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through, is emitted from, or is reflected from a particular area, and falls wit ...
'' 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.
Brightness
in Federal Standard 1037C, the ''Federal Glossary of Telecommunication Terms'' (1996)
With regard to
star A star is an astronomical object comprising a luminous spheroid of plasma held together by its gravity. The nearest star to Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life ...
s, brightness is quantified as apparent magnitude and
absolute magnitude Absolute magnitude () is a measure of the luminosity Luminosity is an absolute measure of radiated electromagnetic power (light), the radiant power emitted by a light-emitting object over time. In astronomy Astronomy () is a natura ...
. Brightness is an antonym of dimness or dullness.

# New meaning

The United States
Federal Trade Commission The Federal Trade Commission (FTC) is an independent agency of the United States government whose principal mission is the enforcement of civil (non-criminal) antitrust law Competition law is the field of law that promotes or seeks to maint ...
(FTC) has assigned an unconventional meaning to brightness when applied to lamps. When appearing on light bulb packages, brightness means luminous flux, while in other contexts it means luminance. Luminous flux is the total amount of light coming from a source, such as a lighting device. Luminance, the original meaning of brightness, is the amount of light per solid angle coming from an area, such as the sky. The table below shows the standard ways of indicating the amount of light.