emissivity

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em·is·siv·i·ty

 (ĕm′ĭ-sĭv′ĭ-tē)
n.
The ratio of the radiation emitted by a surface to the radiation emitted by a blackbody at the same temperature.
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

emissivity

(ɪmɪˈsɪvɪtɪ; ˌɛm-)
n
(General Physics) a measure of the ability of a surface to radiate energy; the ratio of the radiant flux emitted per unit area to that emitted by a black body at the same temperature. Symbol: ε
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014

em•is•siv•i•ty

(ˌɛm əˈsɪv ɪ ti, ˈi mə-)

n.
the ability of a surface to emit radiant energy compared to that of a black body at the same temperature and with the same area.
[1875–80]
Random House Kernerman Webster's College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.
Translations
References in periodicals archive ?
The longwave radiation exchange between the glass and the shade can be characterized by treating the problem as one of graybody radiation exchange with essentially the same geometric interpretation as for shortwave radiation.
If the emissivity is not unity, but is independent of wavelength, then the exitance of this graybody follows Eq.
Conventional mid-infrared sources used in FTIR instruments are thermal emission elements that produce a graybody spectrum from a filament heated to 1000 to 2000 K.