radiance

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The quality or state of being radiant.
• noun Physics The radiant energy emitted per unit time in a specified direction by a unit area of an emitting surface.

from The Century Dictionary.

• noun Brightness shooting in rays or beams; hence, in general, brilliant or sparkling luster; vivid brightness.
• noun Radiation.
• noun Synonyms Radiance, Brilliance, Brilliancy, Effulgence, Refulgence, Splendor, Luster. These words agree in representing the shooting out of rays or beams in an Impressive way. Radiance is the most steady; it is generally a light that is agreeable to the eyes: hence the word is often chosen for corresponding figurative expressions: as, the radiance of his cheerfulness; the radiance of the gospel. Brilliance represents a light that is strong, often too strong to be agreeable, and marked by variation or play and penetration: as, the brilliance of a diamond or of fireworks. Hence, figuratively, the brilliancy of the scene at a wedding; the radiance of humor, the brilliancy of wit. Brilliance is more often literal, brilliancy figurative, Effulgence is a splendid light, seeming to fill to overflowing every place where it is—a strong, flooding, but not necessarily intense or painful light: as, the effulgence of the noonday sun; the effulgence of the attributes of God. Hence a courtier might by figure speak of the effulgence of Queen Elizabeth's beauty. Befulgence is often the same as effulgence, but sometimes weaker. Splendor, which is more often used figuratively is, when used literally, about the same as refulgence. Luster is the only one of these words which does not imply that the object gives forth light; luster may be used where the light is either emitted or reflected, but latterly more often reflected: as, the luster of silk. Luster is generally, like brilliance, a varying light, but it may be simply two or three degrees weaker than splendor. For comparison with glisten, glitter, etc., see glare, v. i.

from the GNU version of the Collaborative International Dictionary of English.

• noun The quality of being radiant; brilliancy; effulgence; vivid brightness.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun the quality of being radiant, shining, bright or splendid
• noun physics the flux of radiation emitted per unit solid angle in a given direction by a unit area of a source

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun an attractive combination of good health and happiness
• noun the amount of electromagnetic radiation leaving or arriving at a point on a surface
• noun the quality of being bright and sending out rays of light