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Perception of light level
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
. 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.
[2]
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
luminance
in
display 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.
- ^
The symbols in this column denote
dimensions
; "
L
", "
T
" and "
J
" are for length, time and luminous intensity respectively, not the symbols for the
units
litre, tesla and joule.
- ^
Standards organizations
recommend that photometric quantities be denoted with a subscript "v" (for "visual") to avoid confusion with radiometric or
photon
quantities. For example:
USA Standard Letter Symbols for Illuminating Engineering
USAS Z7.1-1967, Y10.18-1967
- ^
a
b
c
Alternative symbols sometimes seen:
W
for luminous energy,
P
or
F
for luminous flux, and
ρ
for luminous efficacy of a source.
See also
[
edit
]
References
[
edit
]
External links
[
edit
]
Media related to
brightness
at Wikimedia Commons
Look up
brightness
in Wiktionary, the free dictionary.