View source for Etendue

{{also|étendue}}
==English==
{{was wotd|2017|December|22}}
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===Etymology===
[[File:Ampoule - 2016 01.jpg|thumb|upright|An [[incandescent lamp]]. In [[optics]], etendue is a [[measure#Noun|measure]] of how “spread out” light that crosses, or is [[emit]]ted by, a [[surface#Noun|surface]] is, in terms of [[angle#Noun|angle]] and [[area]].]]

Borrowed from {{bor|en|fr|étendue||area, expanse; size; extent, range, scale}}, short for {{m|fr|[[étendue]] [[géométrique]]||geometric extent}}.

===Pronunciation===
* {{IPA|en|/ˌeɪ.tɒnˈd(j)uː/|a=RP}}
** {{audio|en|LL-Q1860 (eng)-Vealhurl-etendue.wav|a=Southern England}}
* {{IPA|en|/ˌeɪ.tɑnˈdu/|a=GA}}
* {{rhymes|en|uː|s=3}}
* {{hyphenation|en|eten|due}}

===Noun===
{{en-noun|-}}

# {{lb|en|optics}} A [[conserved#Adjective|conserved]] [[property]] of the [[light#Noun|light]] in an [[optical]] [[system]] which [[characterize]]s how "spread out" the light is in terms of [[angle#Noun|angle]] and [[area]]: it is the [[product]] of its [[cross-sectional]] area ([[normal]] to the [[direction]] of [[propagation]]) and the [[solid angle]] it [[subtend]]s.
#: {{syn|en|AΩ product|acceptance|geometric extent|light-collecting power|light-gathering power|light grasp|optical extent|throughput}}
#* {{quote-book|en|chapter=Advanced Infrared Technology &#91;course title&#93;|chapterurl=https://books.google.com/books?id=EpSfAAAAMAAJ&pg=PP5|title=The University of Michigan Engineering Summer Conferences: Fundamentals of Infrared Technology, June 6–10, 1966; Advanced Infrared Technology, June 27&nbsp;– July 1, 1966; Precision Radiometry&nbsp;– Calibration and Instrumentation, June 27&nbsp;– July 1, 1966: Three Intensive One-week Courses for: Engineers, Scientists|series=University of Michigan Official Publication|location=Ann Arbor, Mich.|publisher=w:University of Michigan|year=1966|volume=67|issue=115|oclc=24801012|passage=The topics include {{...}} carefully outlining the concepts of '''etendue''', finesse, and their theoretical implications; methods of spectral, spatial, temporal, and polarization discrimination; and application of these topics to search and track systems.}}
#* {{quote-book|en|author=w:Wolfgang Demtröder|chapter=Spectroscopic Instrumentation|title=Laser Spectroscopy: Basic Concepts and Instrumentation|series=Advanced Texts in Physics|edition=3rd|location=Berlin|publisher=[[w:Springer Science+Business Media|Springer-Verlag]]|year=2003|page=149|pageurl=https://books.google.com/books?id=lfTxCAAAQBAJ&pg=PA149|doi=10.1007/978-3-662-05155-9|isbn=978-3-662-05157-3|issn=1439-2674|passage=The light power transmitted to the detector is proportional to the product of the solid angle <math>\mathit{\Omega}</math> and area <math>A</math> in the central plane, which is imaged by the lens onto the aperture (often called the '''''étendue''''' <math>U</math>).}}
#* {{quote-book|en|author=Kazuya Ota; Yukata Watanabe; Vadim Banine; Hans Franken|chapter=EUV Source Requirements for EUV Lithography|editor=Vivek Bakshi|title=EUV Sources for Lithography|location=Bellingham, Wash.|publisher=[[w:SPIE#SPIE Press|SPIE Press]]|year=2006|section=section 2.2.6 (Etendue of Source Output and Positioning Stability)|pages=36–37|pageurl=https://books.google.com/books?id=ZUpkOM-FfWIC&pg=PA36|isbn=978-0-8194-5845-2|passage='''Etendue''' is an optical invariant and is called by many different names. One of the names is "light-gathering power." As implied by this terminology, when light enters an optical system with smaller '''etendue''' from another optical system with larger '''etendue''', the former optical system fails to transmit some part of the light. {{...}} Therefore, a given EUV [extreme ultraviolet] power with a larger '''etendue''' than that of the requirement is substantially equivalent to a smaller EUV power with the '''etendue''' of the requirement.}}

====Alternative forms====
* {{l|en|étendue}}

====Translations====
{{trans-top|conserved property of the light in an optical system}}
* Bulgarian: {{t|bg|геометричен фактор|m}}
* Finnish: {{t|fi|akseptanssi}}
* French: {{t|fr|étendue de faisceau|f}}, {{t|fr|étendue géométrique|f}}
* German: {{t|de|Etendue}}
* Italian: {{t|it|accettanza}}
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