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Brightness is an attribute of visual perception in which a source appears to be radiating or reflecting light. In other words, brightness is the perception elicited by the luminance of a visual target. It is not necessarily proportional to luminance. This is a subjective attribute/property of an object being observed and one of the color appearance parameters of color appearance models. Brightness refers to an absolute term and should not be confused with Lightness.
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 *berhtaz, ultimately from a PIE root with a closely related meaning, *bhereg- "white, bright". "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.
A given target luminance can elicit different perceptions of brightness in different contexts; see, for example, White's illusion.
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, at least in some respects, the antonym of darkness.
The United States Federal Trade Commission (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.
|Name||Symbol[nb 1]||Name||Symbol||Symbol[nb 2]|
|Luminous energy||Qv [nb 3]||lumen second||lm⋅s||T⋅J||The lumen second is sometimes called the talbot.|
|Luminous flux, luminous power||Φv [nb 3]||lumen (= candela steradians)||lm (= cd⋅sr)||J||Luminous energy per unit time|
|Luminous intensity||Iv||candela (= lumen per steradian)||cd (= lm/sr)||J||Luminous flux per unit solid angle|
|Luminance||Lv||candela per square metre||cd/m2||L−2⋅J||Luminous flux per unit solid angle per unit projected source area. The candela per square metre is sometimes called the nit.|
|Illuminance||Ev||lux (= lumen per square metre)||lx (= lm/m2)||L−2⋅J||Luminous flux incident on a surface|
|Luminous exitance, luminous emittance||Mv||lux||lx||L−2⋅J||Luminous flux emitted from a surface|
|Luminous exposure||Hv||lux second||lx⋅s||L−2⋅T⋅J||Time-integrated illuminance|
|Luminous energy density||ωv||lumen second per cubic metre||lm⋅s⋅m−3||L−3⋅T⋅J|
|Luminous efficacy||η [nb 3]||lumen per watt||lm/W||M−1⋅L−2⋅T3⋅J||Ratio of luminous flux to radiant flux or power consumption, depending on context|
|Luminous efficiency, luminous coefficient||V||1||Luminous efficacy normalized by the maximum possible efficacy|
|See also: SI · Photometry · Radiometry|
The term "brightness" is also used in discussions of sound timbres, in a rough analogy with visual brightness. 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.
Media related to brightness at Wikimedia Commons
|Look up brightness in Wiktionary, the free dictionary.|