Brightness is an attribute ofvisual perception in which a source appears to be radiating/reflectinglight.[1] In other words, brightness is theperception dictated by theluminance of a visual target. The perception is not linear to luminance, and relies on the context of the viewing environment (for example, seeWhite's illusion).
Brightness is a subjective sensation of an object being observed and one of thecolor appearance parameters of manycolor appearance models, typically denoted as. Brightness refers to how much lightappears to shine from something. This is a different perception thanlightness, which is how light something appearscompared to a similarly lit white object.[2]
The adjectivebright derives from an Old Englishbeorht with the same meaning via metathesis giving Middle Englishbriht. The word is from aProto-Germanic*berhtaz, ultimately from aPIE root with a closely related meaning, *bhereg- "white, bright"."Brightness" was formerly used as a synonym for thephotometric termluminance and (incorrectly) for theradiometric termradiance. As defined by the USFederal 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 tostars, brightness is quantified asapparent magnitude andabsolute magnitude.
Twopictograms resembling the Sun with rays are used to represent the settings ofluminance indisplay devices. They have been encoded inUnicode 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 StatesFederal Trade Commission (FTC) has assigned an unconventional meaning to brightness when applied tolamps. When appearing on light bulb packages, brightness meansluminous 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 | ||
| Luminous energy | Qv[nb 3] | lumen second | lm⋅s | T⋅J | The lumen second is sometimes called thetalbot. |
| Luminous flux, luminous power | Φv[nb 3] | lumen (= candelasteradian) | lm (= cd⋅sr) | J | Luminous energy per unit time |
| Luminous intensity | Iv | candela (= lumen per steradian) | cd (= lm/sr) | J | Luminous flux per unitsolid angle |
| Luminance | Lv | candela per square metre | cd/m2 (= lm/(sr⋅m2)) | L−2⋅J | Luminous flux per unit solid angle per unitprojected source area. The candela per square metre is sometimes called thenit. |
| Illuminance | Ev | lux (= lumen per square metre) | lx (= lm/m2) | L−2⋅J | Luminous fluxincident on a surface |
| Luminous exitance, luminous emittance | Mv | lumen per square metre | lm/m2 | L−2⋅J | Luminous fluxemitted 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/m3 | L−3⋅T⋅J | |
| Luminous efficacy (of radiation) | K | lumen perwatt | lm/W | M−1⋅L−2⋅T3⋅J | Ratio of luminous flux toradiant flux |
| Luminous efficacy (of a source) | η[nb 3] | lumen perwatt | 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 | ||
| See also: | |||||
Media related tobrightness at Wikimedia Commons
Authority control databases: National |
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