We found this modulated light transmitter circuit in the Radio Craft magazine of January 1939. Despite the inertia of the filament, it used an incandescent lamp in the transmission, which greatly limited the passband. Filament lamps can be used in this transmission mode up to a few hundred hertz, which makes communication barely understandable. For a perfect version you can think of a modern version using LEDs. The receiver is the next design.
