Who Invented the Twisty Little Bit of Wire Inside the Light Bulb?

We all learned in our history classes that Thomas Edison invented the light bulb in 1879 and that the first successful filament was a carbonized piece of cotton thread that burned for 13.5 hours. Today, light bulb filaments are not something we think about, unless they burn out, but their early development is a fascinating story of 19^th century chemistry and materials science.

Edison decided to develop an incandescent lighting system at a time when he was acknowledged as the nationπs foremost inventor of telegraphic equipment. By the fall of 1877 Edison had developed some critical insights and announced to the press that he would soon have a commercially successful system.

He concluded that a current regulator was needed prevent the bulbπs filament from overheating. Either a thermal expansion device or telegraph style relay could be used to open the circuit when the current was too high. Circuit breakers protecting each filament meant that light bulbs would need to be wired in parallel.

Fortunately Edison knew enough about Jouleπs and Ohmπs laws to recognize that high-resistance lamps would work most efficiently in parallel circuits. Experiments carried out in the Menlo Park, New Jersey, laboratories, revealed that a filamentπs energy consumption was proportional to its radiating surface, not its resistance. In other words, high resistance lamps would not require more energy than low resistance ones. Decreasing the radiating surface actually produced more light. Thus the ideal filament would be a long, thin wire with high resistance. And once he reached this point in October of 1878, Edison believed that the incandescent light was as good as already invented.

By the time Edison had started his lighting project in 1877, some twenty inventors had already built light bulbs with either platinum or iridium filaments heated in air, or carbon filaments heated in a vacuum. Platinum was the ideal material. It had a high melting point, could be wound in a tight coil, and resisted oxidation. Carbon on the other hand was too easily oxidized and difficult to protect with the current vacuum technologies. Earlier inventors tried unsuccessfully to get around this problem by using carbon filaments in nitrogen and even hydrocarbon atmospheres.

To overcome platinumπs expense Edison tried to find new sources and develop platinum alloys. Both efforts failed, as did attempts to use less expensive metals. By this time the press, which had come to expect miracles from Edison, (a view which Edison himself strongly encouraged) was becoming impatient for results.

It is well beyond the scope of this article to describe Edisonπs 1878 work on electrical generators, generating publicity, and how financial backing was arranged for the incandescent lighting system. Suffice to say that these efforts were critical for bringing the project to completion.

It was while working with metallic filaments that Edison and his staff made one of their most important contributions to chemistry. Microscopic and chemical examinations of platinum/iridium alloy filaments that had been heated in air revealed that oxidation was a major problem. The metal seemed to adsorb gasses during heating and that its melting point depended on the amount of gas in its pores. What was obviously needed was a better vacuum pump.

By combing the scientific literature the Menlo Park staff learned that the two best pumps were the Sprengel and Geissler mercury types. Unable to acquire them, Edison commissioned a glass blowing firm to build new pumps that combined the best features of both. A McLeod gauge was added and the laboratory soon had the worldπs most efficient (though sometimes temperamental) vacuum pump.

Heating platinum in a better vacuum degassed the filaments and in turn enabled them to be thinner and to withstand higher temperatures. It would also make the system cheaper since individual circuit breakers were no longer needed for each lamp.

Edison eventually presented his work on gasses in metals to the American Association for the Advancement of Science. It is recognized as a major contribution to the chemistry of metals. All of this work however did not solve the problem of platinumπs cost.

Armed with a better vacuum pump, Edison now turned to carbon as a potential filament. He sought a naturally occurring fiber that could be carbonized. Among the many fibers tried were human hairs, animal hairs, thinly sliced horn, all kinds of threads, and botanical specimens from around the world. In order to improve their strength, Edison tried impregnating the carbonized fibers with rock candy, whale oil, cotton oil, and any number of hydrocarbons. Ultimately, the most successful fiber proved to be thinly sliced strips of bamboo.

Meanwhile, the press, public, and financial backers were growing impatient. Edison needed light bulbs for his demonstration projects. And so the first bulbs had carbonized paper filaments. Even the finest paper had an irregular distribution of fibers and varied in thickness. Paper filaments only lasted about 300 hours.

It is at this point that the research split into two very different paths. Inspired by the nineteenth century ideal of a bounteous natural world that was filled with good things for all mankind, Edison sought a natural fiber somewhere in ≥Godπs almighty workshop.≤ His rivals attempted to create a synthetic one.

As they saw it, only an amorphous, dense, and completely uniform carbon filament would provide long lasting illumination. No natural fiber could ever meet these requirements.

Edisonπs two principle rivals were William Sawyer of New York and Edward Weston of Newark, New Jersey. Weston was a native of England who came to the United States as a young man of twenty in 1870. He settled in New York where his first position was with a manufacturer of photographic chemicals. The chance to revamp an almost-bankrupt plating company led Weston into the field of electrochemistry. Since at that time there was no reliable source of electric current, Weston began building his own dynamos, which in turn became his primary business.

He moved to Newark, New Jersey in 1875 and by 1877 had acquired a former synagogue on Washington Street for use as the nation's first electrical machinery plant. Armed with good dynamos and a very thorough knowledge of chemistry, Weston took up the challenge of electric lighting a year before Edison.

Many readers of the Indicator will recognize Weston as the inventor of the Normal Cell (the fist standard unit of a volt) and founder of the Weston Instrument Company, one of the worldπs foremost electrical instrumentation manufacturers. Both of these achievements were in the future.

Although his first commercial successes would be with outdoor arc lights, Weston also worked to develop an incandescent light for indoor use. His first light bulb filaments were made by squeezing a mixture of carbon dust and tar through a narrow aperture. But when these fibers proved non-homogeneous, Weston thought back to his days as a photographic chemist and resolved to try celluloid.

Celluloid is made by combining nitrated cellulose with camphor under high heat and pressure. Because it is highly flammable, a stable form was required for use as a filament. Weston reasoned that since the starting material had been oxidized, treatment with a reducing agent would de-nitrify and convert the celluloid back into cellulose. In September of 1882, he patented a process where celluloid was immersed in baths containing hydrated ammonium sulphide, ferrous chloride, or ferrous sulphate. According to the inventor, the resulting material was non-flammable, dense, flexible, and tough.

Filaments were cut from sheets of this material, which Weston named ≥Tamidine≤. The filaments were heated to remove the dissolved gasses, carbonized, and finally had the ends plated in copper.

Unlike Weston who was a trained scientist, and Edison who was a highly disciplined researcher, William Sawyer was a journalist and part time inventor of telegraph equipment. Despite limited financing, poor theoretical understanding, and a drinking problem, Sawyer did manage to produce a working light bulb with a carbon filament. But he and his backers rushed their bulbs into production without first taking the time to refine their product or their production techniques. They were forced to quit the project by June of 1878.

Sawyer did create one process that was vital to the production of carbon filaments, he made them ≥self repair.≤ Gently heating the filaments in a hydrocarbon atmosphere caused the weak spots and surface pockmarks to heat up and glow brightly. Carbon was deposited on these spots until the entire filament had a uniform cross section. Weston made the same discovery at about the same time but Sawyer was first to patent the process.

Meanwhile, back at Menlo Park, Edison had not been idle. Once bamboo was found to be an effective filament, another search was made for the optimal species. First, specimens of all tropical grass species that could be obtained in the United States were tried. Agents were then sent to Cuba and South America to hunt for tropical grasses. William H. Moore was sent to Japan and China to obtain more exotic varieties of bamboo. After an exhaustive search, a contract was signed with a Japanese grower near Kyoto. Before the end of the filament search, some 6000 species of bamboo had been tried.

Trained scientists shook their heads over Edisonπs bamboo search and his detractors have pointed to the effort as a monumental waste of time. They missed an important point, even if the search failed to generate a single usable filament, it did generate huge amounts of publicity. Edison made a point of being on the pier whenever one of his filament hunters returned home, then with the press watching, he loudly questioned the man about his results. Edison was also an avid reader of Jules Verneπs novels and the worldwide search through mountains and jungles was like living out one of Verneπs plots.

And the Japanese filaments did work well. By 1880, Edison was producing bulbs that could last up to 1500 hours.

Even as the last of Edisonπs filament hunters were returning to New Jersey, the industrialist Hiram Maxim (later famous for his machine guns) was manufacturing bulbs with Tamidine filaments. Patent royalties from these filaments proved immensely valuable to Weston. Lasting up to 2000 hours, Tamidine quickly became a serious competitive challenge for bamboo and other plant fibers. Until the introduction of tungsten filaments, many of the worldπs light bulbs were made with this material.

In 1906, General Electric introduced incandescent bulbs with tungsten filaments.

Of the twenty or so inventors who had worked on incandescent lights before Edison, most are remembered only in the better history books. Edward Weston may have had the better filament but lacked Edisonπs impressive financial backing and favorable press. Although he was awarded the contracts for lighting Newarkπs streets and later the Brooklyn Bridge, Weston eventually dropped out of the lighting business and turned his attention to electrical measuring instruments. The Weston Instrument Company was founded in 1888. Their factory at the corner of Newarkπs Plane and Orange Streets turned out thousands of instruments. Westonπs patent portfolio included advances in electroplating, electrical meters, fuses, batteries, and motors. The growing fame of Westonπs Newark research laboratory is said to have goaded Edison into abandoning Menlo Park and constructing the huge research facilities in West Orange, New Jersey.

In recent years, the story of the light bulb has attracted scholarly attention and even a Smithsonian Exhibition. For readers interested in learning more, I recommend Edison's Electric Light: Biography of an Invention by Robert Douglas Friedel and Edison, A Life of Invention by Paul Israel.