The Photophone, also known as a radiophone, was invented jointly by Alexander Graham Bell and his then-assistant Charles Sumner Tainter on February 19, 1880, at Bell's 1325 'L' Street laboratory in Washington, D.C. Both were later to become full associates in the Volta Laboratory Association, created and financed by Bell.
On June 3, 1880, Alexander Graham Bell transmitted the first wireless telephone message on his newly invented "photophone." Bell believed the photophone was his most important invention. The device allowed for the transmission of sound on a beam of light. Of the eighteen patents granted in Bell's name alone, and the twelve he shared with his collaborators, four were for the photophone.