The inventive ingenuity of others brought in time better and more economical incandescent lamps. From the filaments of bamboo fiber the next step was to filaments of cellulose in the form of cotton, duly prepared and carbonized. Later (1905) came the metalized carbon filament and finally the employment of tantalum or tungsten. The tungsten lamps first made were very delicate, and it was not until W. Coolidge, in the research laboratories of the General Electric Company at Schenectady, invented a process for producing ductile tungsten that they became available for general use.英文原著 · 《The Age of Invention》