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Phrase(s): dim something up
to use a dimmer to make the lights brighter. (Theatrical. A dimmer is a rheostat, variable transformer, or something similar. The expression, a seeming contradiction, is the opposite of dim something down.) • As the curtain rose, the electrician dimmed the lights up on a beautiful scene. • You dimmed up the lights too fast.
McGrawhill's American Idioms And Phrasal Verbs