Evolution of the incandescent carbon filament

The incremental improvements to the design and manufacture of carbon filaments from the first incandescent lamps up to the adoption of the tungsten filament are too numerous to count. We can at least get an understanding of what the most important innovations were by examining the historical literature dedicated to the development of the incandescent light. It is clear, from a review of the sources listed further down this page, that four major developments stood out above the others:

  1. "Carbonizing" an organic fiber or thread. Joseph Swan and Thomas Edison developed methods of heating an organic thread (such as a cotton thread or bamboo fiber) in a closed furnace until only a carbon skeleton remained. This technique produced the carbon filaments used in the earliest successful incandescent light bulbs.
  2. Hydrocarbon "flashing" process. The quality of the carbon filament was greatly improved by immersing it in an atmosphere of hydrocarbon gas and heating it with an electric current. Carbon deposits would build up on the thinnest, weakest spots on the filament, until all areas of the filament were of uniform width and resistance. This "flashing" process, which improved the efficiency and duration of the electric light, was originally patented by William Sawyer and Albon Man. Other inventors patented similar processes for use in connection with their own lamps.
  3. Cellulose filament. The natural fibers used to make filaments were eventually superseded by artificially produced fibers made of amorphous cellulose. To manufacture the filaments, some cotton or other fibrous organic substance was chemically dissolved into a liquid cellulose solution which was then extruded into fibers and carbonized. The result was a tough, dense carbon filament that not only improved lighting efficiency, but also lent itself well to mass production techniques for the manufacture of incandescent lamps. Engineers and scientists who developed methods of making cellulose filaments include Joseph Swan, Desmond Fitzgerald, Edward Weston, and Leigh S. Powell.
  4. General Electric Metallized (GEM) filament. Willis R. Whitney in 1904 invented a new heating process which hardened the surface of the filament and led to reduced evaporation of the carbon. The ability to operate the lamp at higher temperatures increased the efficiency (lumens/watt) by about 25% over a regular carbon lamp.

The carbon filament became obsolete after the introduction of the tungsten filament.

Sources

The following references cover the early development of filament manufacture. None of them mentions Lewis Latimer's work.

John Howell and Henry Schroeder, History of the incandescent lamp (Schenectady, N. Y.: The Maqua Company, 1927) Chapter 3 is titled "Development of Filaments."

Arthur A. Bright, The electric-lamp industry; technological change and economic development from 1800 to 1947 (New York, Arno Press, 1972 [c1949]) Much historical information about filaments throughout the book.

"Lighting", Encyclopedia Britannica (1911 ed.) Outlines the major steps in the evolution of the carbon filament.

James A. Cox, A century of light (New York : Benjamin, c1979) Contains short overview of how the filament evolved.

Matthew Luckiesh, Torch of civilization (New York: G. P. Putnam's Sons, c1940) The "Glowing Filaments" chapter treats the history of the filament.

What about Lewis Latimer?

Lewis Latimer's "Process of Manufacturing Carbons," patented in 1882 (US Patent #252386), was not so much a new process as an incremental improvement of the old one that was already being used at Hiram Maxim's US Electric Lighting Company where Latimer worked. Latimer's idea was to protect the filaments in special envelopes as they were carbonized, in order to reduce the chance of breakage during the process. There is a common misconception that Latimer made a new kind of filament, or a "longer lasting" filament -- but nowhere in the patent did Latimer suggest that the practice would improve the performance of the filament by any noteworthy degree. His stated purpose in the patent was to make the filaments less likely to break or change shape during manufacture. Latimer's obituary in Electrical World (Dec. 22, 1928) noted a "successful method of producing carbon filaments for the Maxim incandescent lamp" as among his career accomplishments; however, there is no reason to assume that his method was adopted by other light manufacturers (such as Edison's company) which had their own manufacturing processes.

Another Latimer patent (US #247,097), issued in 1881 to Latimer and co-inventor Joseph Nichols (both of the United States Electric Lighting Company) for an alternative way of securing the carbon filament to metallic lead wires, was very similar to an earlier patent (US #244481) by Charles Perkins of the same company. Perkins attached flat metal conductors to the lead wires and bent the conductors around the flattened ends of the filament; Nichols and Latimer did a similar thing but bent the conductors through holes in the flattened ends of the filament. Other methods of attachment were developed during the same time, the most common being to copperplate the ends of the filament to the lead wires. The copperplating method dominated until about 1886 when carbon paste adhesive started being used.