Lightguide display

Light from independently controlled incandescent bulbs passing into the edge of these panels reflects off the internal surfaces of the plastic.

[1] But the need for digit read-out arose with electronic computers in the 1950s with many independent inventions, both in edge-lighting, nixie tubes and other technologies.

U.S. patent 2,751,584 for an edge-lit multi-layer digit "Visual readout device" was filed on November 10, 1953, by inventor Carl L. Isborn of Hawthorne, California, for the National Cash Register Company and granted on June 19, 1956.

[1] For a similar invention of a "Visual in-line multi-symbol signal indicator", U.S. patent 2,766,447 was filed on July 7, 1954, by Wesley E. Woodson, Jr., El Cajon, and Jack I. Morgan of San Diego, California, and granted on October 9, 1956.

[1] U.S. patent 2,813,266 for an "Indicator device and means for mounting" was filed on January 9, 1956, by Andrew F. Kay, Covert B. Meredith, and Leonard M. Scholl of San Diego County, California, and granted on November 12, 1957.

A lightguide (edge-lit) display.
The Swedish electronic computer BESK , built in 1953, displayed 18 hexadecimal digits using edge-lit acrylic, the grey squares at the center of the green console.
Light guide LEDs using plastic light guides on a network switch