Scophony Ltd., based in London, produced a number of innovations in large-screen projectors. Most notably was the development of a light valve that used piezoelectric crystals to produce ultrasonic standing waves in a tube of liquid. When light was passed through the liquid, the standing waves caused the light to refract similar to today's GLV devices. The waves traveling thought the tube acted as a crude "video memory" so a segment of a line could be reproduced simultaneously, resulting in much higher screen brightness than with a single moving spot.