Brightness is an attribute of visual perception in which a source appears to be radiating or reflecting light.[1] In other words, brightness is the perception elicited by the luminance 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 
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.[3] Brightness is an antonym of "dimness" or "dullness".
With regard to stars, brightness is quantified as apparent magnitude and absolute magnitude.
Two pictograms resembling the Sun with rays are used to represent the settings of luminanceindisplay devices. They have been encoded in Unicode since version 6.0 (October 2010) in the Miscellaneous Symbols and Pictographs block under U+1505 as "low brightness symbol" (🔅) and U+1F506 as "high brightness symbol" (🔆).[4]
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.[5] 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.
Quantity
Unit
Dimension
[nb 1]
Notes
Name
Symbol[nb 2]
Name
Symbol
Qv[nb 3]
lm⋅s
T⋅J
The lumen second is sometimes called the talbot.
Luminous flux, luminous power
lm (= cd⋅sr)
J
Luminous energy per unit time
Iv
candela (= lumen per steradian)
cd (= lm/sr)
J
Luminous flux per unit solid angle
Lv
cd/m2 (= lm/(sr⋅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.
Ev
lux (= lumen per square metre)
lx (= lm/m2)
L−2⋅J
Luminous flux incident on a surface
Luminous exitance, luminous emittance
Mv
lumen per square metre
lm/m2
L−2⋅J
Luminous flux emitted from a surface
Hv
lx⋅s
L−2⋅T⋅J
Time-integrated illuminance
Luminous energy density
ωv
lumen second per cubic metre
lm⋅s/m3
L−3⋅T⋅J
Luminous efficacy (of radiation)
K
lumen per watt
lm/W
M−1⋅L−2⋅T3⋅J
Ratio of luminous flux to radiant flux
Luminous efficacy (of a source)
lumen per watt
lm/W
M−1⋅L−2⋅T3⋅J
Ratio of luminous flux to power consumption
Luminous efficiency, luminous coefficient
V
1
Luminous efficacy normalized by the maximum possible efficacy
Media related to brightness at Wikimedia Commons
