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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Example sentences
But a close look at this upward escaping luminosity can reveal cultural clues
  about the polluters.
Look where you will, you shall find the producer acquiring what luminosity he
  can, that the product may thence take profit.
And that should be enough, since luminosity and temperature are related.
The luminosity of the immediate moment is framed, if not altogether blotted
  out, by the shadows of past and future.
Image for luminosity
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