Light Pictures

General Electric physicists long ago learned how to talk along a beam of light. Last week they showed how light might carry television pictures.

The light-telephone, devised by John Bellamy Taylor, translates sound into electrical impulses (as does an ordinary telephone) and then through a neon bulb into a pink wave of light. The receiving set catches the light in a photoelectric tube which translates the message into electricity, then sound. Dr. Taylor has telephoned by this system across the Hudson River, a distance of about 3,000 ft. Anyone with a proper receiving set who could see his sending beam, could hear what he said.

The light-television apparatus, developed by Dr. Ernst Frederik Werner Alexanderson, derives its carrier wave from a high-intensity arc light. The carrier wave is modulated by the Alexanderson scanning device which translates a picture or scene into electricity (TIME, Jan. 23, 1928). As with the Taylor system, anyone who has the proper receiving apparatus and can see the Alexanderson beam, can also see what the television apparatus is seeing.

For local broadcasts either system might be used. But the Taylor neon tube system could be used by only one visible station at a time, because the receivers see every modulated beam of neon light striking them and would be hopelessly confused by two or more sending beacons.

The Alexanderson arc, however, can modify as well as modulate the carrier light waves. Hence receivers could tune in on properly differentiated sending lights.

Both systems are still playthings. Yet some day, Dr. Alexanderson imagined last week, "we may see television broadcast from a powerful arc light, mounted atop a single tower high above the city. . . . These light waves can be received at relatively short distances only, perhaps ten miles; each community could then have its light broadcasting system. Light broadcasting may have the same relation to radio broadcasting as the local newspaper has to the national newspapers."

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