the quality of being bright.

Optics . the luminance of a body, apart from its hue or saturation, that an observer uses to determine the comparative luminance of another body. Pure white has the maximum brightness, and pure black the minimum brightness.

noun

dullness , darkness , stupidity

noun

luster , illumination , light , luminosity , shine , brilliance , glaze , gloss , smarts , acumen , aptitude , competence , iq , acuteness , animation , aptness , brilliancy , clarity , clearness , discernment , effulgence , flame , gleam , glow , liveliness , precocity , radiance , refulgence , resplendence , sharpness , sheen , sparkle , splendor , vivacity