From radiant + -ance.

• IPA: /ˈɹeɪdi.əns/

radiance

1. The quality or state of being radiant; shining, bright or splendid.
   • 1667, John Milton, “Book VII”, in Paradise Lost. […], London: […] [Samuel Simmons], and are to be sold by Peter Parker […]; [a]nd by Robert Boulter […]; [a]nd Matthias Walker, […], →OCLC ↗; republished as Paradise Lost in Ten Books: […], London: Basil Montagu Pickering […], 1873, →OCLC ↗:

     Girt with omnipotence, with radiance crowned.

2. (physics) The flux of radiation emitted per unit solid angle in a given direction by a unit area of a source.

• French: éclat
• German: Glanz, Strahlen, Leuchten
• Italian: radianza
• Portuguese: radiância
• Russian: сия́ние
• Spanish: resplandor, brillo, fulgor

• German: Radianz, Strahldichte
• Portuguese: radiância
• Russian: излуче́ние