luminosity

from WordNet (r) 3.0 (2006)

luminosity
    n 1: the quality of being luminous; emitting or reflecting
         light; "its luminosity is measured relative to that of our
         sun" [syn: {luminosity}, {brightness}, {brightness level},
         {luminance}, {luminousness}, {light}]

from The Collaborative International Dictionary of English v.0.48

Luminosity \Lu`mi*nos"i*ty\, n.
   The quality or state of being luminous; luminousness.
   [1913 Webster]