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Meaning of light valve

light' valve"

Pronunciation: [key]
— Elect. Elect.
  1. a light-transmitting device having transmissions that vary in accordance with an electric input, as voltage, current, or an electron beam, used chiefly for recording sound on motion-picture film.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.