Bell with photophone, holding pipe, and wearing headphones. The photophone (later given the alternate name radiophone) was similar to a contemporary telephone, except that it used modulated light as a means of wireless transmission while the telephone relied on modulated electricity carried over a conductive wire circuit. It was invented jointly by Alexander Graham Bell and his assistant Charles Sumner Tainter on February 19, 1880. Bell believed the photophone was his most important invention. Of the 18 patents granted in Bell's name alone, and the 12 he shared with his collaborators, four were for the photophone, which Bell referred to as his "greatest achievement", telling a reporter shortly before his death that the photophone was "the greatest invention (I have) ever made, greater than the telephone". The master patent for the photophone was issued in December 1880, many decades before its principles came to have practical applications. Alexander Graham Bell (March 3, 1847 - August 2, 1922) was a Scottish-American speech therapist and inventor of the telephone. Photographed by Underwood & Underwood, May 5, 1922.