ell and his assistant Charles Sumner Tainter jointly invented a wireless telephone, named a photophone, which allowed for the transmission of both sounds and normal human conversations on a beam of light.^[123][124] Both men later became full associates in theVolta Laboratory Association.

On June 21, 1880, Bell's assistant transmitted a wireless voice telephone message a considerable distance, from the roof of the Franklin School in Washington, D.C., to Bell at the window of his laboratory, some 213 metres (700 ft) away, 19 years before the first voice radio transmissions.^{[113][125][126][127]}

Bell believed the photophone's principles were his life's "greatest achievement", telling a reporter shortly before his death that the photophone was "the greatest invention [I have] ever made, greater than the telephone".^[128] The photophone was a precursor to thefiber-optic communication systems which achieved popular worldwide usage in the 1980s.^[129][130] Its master patent was issued in December 1880, many decades before the photophone's principles came into popular use.