noun, plural luminosities.
luminance ( def 2 ).
the quality of being intellectually brilliant, enlightened, inspired, etc.: The luminosity of his poetry is unequaled.
something luminous.
Astronomy. the brightness of a star in comparison with that of the sun: the luminosity of Sirius expressed as 23 indicates an intrinsic brightness 23 times as great as that of the sun.
Also called luminosity factor. Optics. the brightness of a light source of a certain wavelength as it appears to the eye, measured as the ratio of luminous flux to radiant flux at that wavelength.

1625–35; < Latin lūminōs(us) luminous + -ity

nonluminosity, noun
self-luminosity, noun Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
luminosity (ˌluːmɪˈnɒsɪtɪ)
n , pl -ties
1.  the condition of being luminous
2.  something that is luminous
3.  astronomy a measure of the radiant power emitted by a star
4.  physics See also colour Former name: brightness the attribute of an object or colour enabling the extent to which an object emits light to be observed

Collins English Dictionary - Complete & Unabridged 10th Edition
2009 © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
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Word Origin & History

1630s, "quality of being luminous," from luminous. In astronomy sense of "intrinsic brightness of a heavenly body" (as distinguished from apparent magnitude, which diminishes with distance), attested from 1906.
Online Etymology Dictionary, © 2010 Douglas Harper
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