brightness

From Middle English bryghtnes, brightnesse, from Old English beorhtnes (“brightness, splendor”), equivalent to bright +‎ -ness.

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brightness (usually uncountable, plural brightnesses)

1. The quality of being bright.
   • 1918, W. B. Maxwell, chapter 5, in The Mirror and the Lamp:

     Here, in the transept and choir, where the service was being held, one was conscious every moment of an increasing brightness; colours glowing vividly beneath the circular chandeliers, and the rows of small lights on the choristers' desks flashed and sparkled in front of the boys' faces, deep linen collars, and red neckbands.

2. The perceived luminance of an object.
3. Intelligence, cleverness.

• See also Thesaurus:intelligence