1. brightness, light, lightness

usage: the location of a visual perception along a continuum from black to white

2. brightness, cleverness, smartness, intelligence

usage: intelligence as manifested in being quick and witty

3. luminosity, brightness, brightness level, luminance, luminousness, light, physical property

usage: the quality of being luminous; emitting or reflecting light; "its luminosity is measured relative to that of our sun"

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See also: brightness (Dictionary)