Edison and Innovation Series-The Big Bonanza: Edison's Electric Lighting System

Year of Innovation - Invention Factory
  1. Conceiving the System
  2. Supporting the Work
  3. The Platinum-Filament Lamp
  4. Designing the Generator
  5. The Carbon-Filament Lamp
  6. Demonstrating the New Light
  7. From Research to Development

By the time Edison began his effort to develop an incandescent electric light in September 1878, researchers had been working on the problem for forty years.  While many of them developed lamps that worked in the laboratory and for short-term demonstrations, none had been able to devise a lamp that would last in long-term commercial use.  Edison was able to succeed where others had failed because understood that developing a successful commercial lamp also required him to develop an entire electrical system. With the resources of his laboratory, he and his staff were able to work simultaneously on the lamp and other elements of the system.

Conceiving the System
Edison briefly experimented with electric lighting in 1877 but he did not begin to focus his attention on the subject until George Barker, physics professor at the University of Pennsylvania, invited him to see the arc light system developed by William Wallace and Moses Farmer at Wallace’s shop in Connecticut. According to the New York Sun reporter who accompanied him on the visit, "Edison was enraptured.  He fairly gloated over it. . . . He ran from the instruments to the lights, and from the lights back to the instrument.  He sprawled over a table with the simplicity of a child, and made all kinds of calculations.  He estimated the power of the instrument and of the lights, the probable loss of power in transmission, the amount of coal the instrument would save in a day, a week, a month, a year, and the result of such saving on manufacturing."

A week later the Sun published Edison’s plans to develop a complete electric lighting system to replace gaslight in lower Manhattan.  He would generate electricity using fifteen or twenty Wallace dynamos run by a 500-horsepower engine and distribute it through underground mains similar to those carrying gas. He would use existing gas pipes to carry his electric wires through buildings and place his lamps in converted gas fixtures.  Customers would be charged by a meter similar to those employed by gas companies.  The use of gas lighting as a model helped Edison determine more than a market for his electrical system, it also affected his technical designs as he sought to make it resemble the older lighting system he planned to replace.

Edison did not provide the details of  his proposed system to the Sun reporter but his early notes and patent caveats indicate that he believed the solution to the problem of "subdividing the light" lay in developing a thermal regulator to prevent the incandescing element of his lamp from melting.  Edison reached this conclusion by thinking of electric lights as analogous to telegraph instruments and treating the lamp regulator as a form of electromechanical switch similar to those he used in multiple telegraph designs.  Having arrived at this solution, Edison began designing lamp regulators in the same fertile manner by which he had previously varied the relays and circuits of his telegraph designs.  His first electric light patent caveat describes "devices whereby the heat arising from the passage of [the] current is utilized to regulate the temperature of the incandescent metal which serves to give the light so that it is never allowed to reach its melting point no matter how strong a current attempts to pass through."

Another key element of Edison’s system was his insight regarding the relationship between high resistance lamps and parallel circuits.  Because the regulator temporarily removed the lamp from the circuit, he had to place the lamps in parallel circuits so that each individual lamp could be turned on and off without affecting any others in the circuit.  This was also desirable for customers used to independently operated gas lamps.  As early as November 1877, Edison had determined that high resistance lamps were best suited for parallel circuits.  When he realized that this arrangement provided the best economy is unclear, but the cost benefits were certainly well understood in the laboratory by the following November when Charles Batchelor wrote of a competing design that it "would want enormous large conductors owing to [the] small resistance" in each lamp."

Edison's ideas regarding lamp resistance grew out of his understanding of basic electrical laws.  He knew that in order to reduce energy lost as excess heat in his distribution system it would be necessary to increase the cross section of his copper conductors but that this would raise their cost and make the system uneconomical.  However, he could reduce the size of the conductors by increasing the voltage proportionately to the current.  This in turn would require him to use high resistance lamps. 

Supporting the Work

Edison’s public pronouncements about his intention to develop an electric lighting system generated considerable interest on the part of several figures connected with Western Union Telegraph who already held him in high regard as an inventor.  Edison was represented in his negotiations with these men by Grosvenor Lowrey, the Western Union attorney who had been acting as his patent attorney in dealing with the company since December 1875.  Because the electric light inventions were independent of any corporate interest by Western Union, Lowrey told Edison "that it will be most for your interest and mine, in dealing with them, that I should act with and for you, entirely; and I shall therefore decline to be interested, and will approach the whole matter from your side of the business."  As negotiations drew to a close during the first days of October, Edison wrote "Friend Lowrey" to tell him to "Go ahead.  I shall agree to nothing promise nothing and say nothing to any person leaving the whole matter to you.  All I want at present is to be provided with funds to push the light rapidly."

These negotiations led to the formation of the Edison Electric Light Company, which was  incorporated in New York City on 16 October.  The incorporators included Western Union president Norvin Green, who became the company president; Hamilton McKay Twombly,  who represented the interests of his father-in-law William H. Vanderbilt, the principal shareholder in Western Union and a heavy investor in gas utilities; Western Union stockholders Tracy Edson and James H. Banker; financier Robert L. Cutting, Jr.; three of Lowrey's law partners; and Egisto Fabbri, a member of Drexel Morgan and Company, the leading American investment bankers with extensive international interests.  Over the next two and half years, Edison Electric would provide $130,000 (approximately $3 million today) for research and development of Edison’s system. Additional funding came from the sale of foreign rights to Drexel Morgan and Egisto Fabbri’s firm, Fabbri and Chauncey, both of which played important roles in the development the Edison system in foreign countries. The international standing of these firms conformed with Lowrey's desire that "the dignity, & importance of the invention to the world, demand that it shall be introduced by men possessing a comparative strength & power in the financial world."  The banking partners, Lowrey assured Edison in January 1879, were "not to be very easily frightened away from a thing they once made up their mind to."

The Platinum-Filament Lamp
Lowrey’s reassurance came amidst reports that Edison had been having difficulties with his  experiments using platinum as a filament.  Like previous experimenters, Edison had focused his initial lamp experiments on two materials—carbon and platinum.  Charred paper or cardboard was a commonly used and cheap carbon material for lamps and Edison used these in his earliest experimental lamps. However, the hand-operated vacuum pump in his laboratory did not create a sufficient vacuum to prevent the carbon from burning up in the atmosphere that remained in the bulb.  Edison instead focused his research on platinum filament lamps that used a regulator to prevent the metal from reaching its melting point.  Although platinum was rare and expensive, it had the highest melting point of any metal other than tungsten, which is used in modern incandescent bulbs.  However, at the time the technology did not exist to draw tungsten into a thin filament.

While Edison’s early platinum-lamp experiments showed promise, he found that his filaments were melting at too low a temperature.  Thus, in January 1879 he conducted basic research on the heating of platinum to find out why this was happening.  His experiments showed that air was absorbed into the pores of the metal as it was heating, causing it to weaken and melt at lower temperatures. To overcome this problem Edison decided to place his metal filament in a vacuum bulb.  Later in the year, Edison presented a paper on this research at the annual meeting of the American Association for the Advancement of Science.

Edison and his assistants had used a mechanical hand pump in some of the early lamp experiments and turned to it again for the new experiments.  However, such pumps provided an inadequate vacuum and the staff began to investigate the state of the art of vacuum technology by searching through scientific and technical journals. The best pumps of the time were Sprengel and Geissler mercury pumps.  After an unsuccessful effort to acquire a Sprengel pump from nearby universities, Edison had a Geissler pump made by the New York glassblowing firm of Reinmann & Baetz. William Baetz also came to Menlo Park periodically to assist in further development of vacuum pumps for the laboratory.  By mid-August he had assembled several different arrangements of Geissler and Sprengel pumps, including combinations of the two based on an article Edison had read; it included a McLeod gauge, which was added to the Menlo Park pump design later in the year.  The advantage of combining the two designs arose from the fact that the Geissler pump produced a vacuum more quickly while the Sprengel pump provided a higher vacuum.  When Baetz turned down an offer to join the laboratory staff, Edison hired Ludwig Boehm, a young glassblower who had worked with Geissler in Germany before immigrating to the United States.  An intense series of experiments in early October led to the development of better and better vacuum pumps.

Using a vacuum improved the performance of Edison’s lamps and he no longer needed to use a regulator to prevent the filaments from melting. However, platinum continued to present problems that were not easily solved. Not only was it a very expensive metal, but platinum also had a relatively low resistance to the electric current. Edison could increase the resistance of his filaments by coiling them into spirals, thus increasing the amount of metal offering resistance to the current. But he had not yet produced low-cost lamps with sufficiently high resistance to make his electrical disribution system economical for widespread use.

Designing the Generator

As Edison and his staff experimented furiously to develop a lamp that would be commercially viable, they also worked on other parts of the electrical system, most notably the generator.  Edison had initially thought that he could use the Wallace arc-light dynamo for his incandescent lighting system.   However, after experimenting with the Wallace and other arc-light dynamos he began to doubt their suitability for incandescent lighting.  Edison began a set of fundamental experiments related to generator design that included extensive experiments with electromagnets intended to produce a fuller understanding of the principles of electromagnetic induction of current.  By the beginning of January 1879, after what Charles Batchelor described as "a few weeks hard study on magneto electric principles," they had advanced their understanding of generators sufficiently that Edison set the machine shop to work building a new design under Batchelor's direction.

During February and March, Edison, Batchelor, and Francis Upton conducted extensive generator experiments that led to a major breakthrough in the design of dynamos for incandescent electric lighting.  Although it is unclear whether these experiments were informed by the important experimental work on generators published by Philadelphia electricians Elihu Thomson and Edwin Houston in late 1878 and early 1879, he and his staff reached the same conclusion—generators with equal internal and external resistence generated maximum current, while those with a small internal resistance produced more efficient power output.

Edison considered the economic efficiency of his system to be related to the number of lamps per horsepower.  He and his staff therefore measured the work output of their generators by employing an electrodynamometer to convert the electrical energy obtained from their generators into foot pounds.  (Thomson and Houston had made similar measurements.)  Edison and his assistants decided that they could design a more efficient dynamo for incandescent lighting by making the internal resistance much smaller than the external load, rather than having equal internal and external resistance as was standard in other generators of the time.  By July Edison could claim that his machine "delivers in the form of current 96% of horse power applied to it. . . .this will give us about 80% of the total horsepower applied that will be useful for lamps."  And Francis Upton wrote to his father "We have now the best generator of electricity ever made and this in itself will make a business."

The Carbon-Filament Lamp
Even though Edison's research on metals and the development of high-vacuum pumps had increased the prospects for the platinum lamp, the use of this rare metal presented Edison with what appeared to be an intractable problem.  Platinum’s high price would make his system uneconomical.  Edison approached this difficulty in a way that became characteristic when he was faced with questions about the commercial availability of a substance that he believed would solve a technical problem—he conducted an exhaustive search for plentiful supplies of the material.  Beginning in the late spring of 1879, he sent out a circular letter to mining districts in the United States and wrote personally to American ambassadors and others in countries with platinum mines.  He also studied geological reports and other literature regarding sources of platinum. Edison spent considerable time during the summer reading and answering the voluminous correspondence which arrived in response from the mining communities of the west and in working with his chemists to assay ores sent to the laboratory.  The most promising source of platinum was tailings from gold mines, and Edison told the secretary of one mining company that he had "4 of my young men working up processes to get the gold and platinum out of the sand taken from the flumes."

Edison's platinum search did not yield a cheap and plentiful source of this rare metal but fortunately the improved vacuum achieved by his laboratory staff enabled him to experiment again with a much cheaper substance—carbon.

Edison and Charles Batchelor spent much of their time during the summer and early fall on telephone experiments to improve the commercial instruments being introduced for use by the newly-formed Edison Telephone Company of London.  The carbon buttons for the transmitters were still being made at the laboratory even though the rest of the instrument as well as the receivers and switchboards were manufactured at Sigmund Bergmann's and other outside shops.  The buttons were made from lampblack scraped off the glass chimneys of a series of kerosene lanterns that were kept burning day and night in a little shed next to the laboratory.  It was the ready availability of this material that led Edison to a fortuitous analogy that prompted him to again try carbon in his lamp. 

Almost from the beginning of the light research, Edison had determined that the most efficient form for his incandescing element would be the thin wire spiral which would allow him to decrease radiating surface and increase resistance.  It was his recognition that the lampblack could be rolled like a wire and then coiled into a spiral like platinum that led Edison to try carbon again as a filament material.  The first newspaper account of his successful carbon lamp describes his "eureka" moment and suggests the analogy that came to his mind:

Sitting one night in his laboratory reflecting on some of the unfinished details, Edison began abstractedly rolling between his fingers a piece of compressed lampblack until it had become a slender thread.  Happening to glance at it the idea occurred to him that it might give good results as a burner if made incandescent.  A few minutes later the experiment was tried, and to the inventor's gratification, satisfactory, although not surprising results were obtained.  Further experiments were made, with altered forms and composition of the substance, each experiment demonstrating that the inventor was upon the right track.

Following two weeks of futile effort by Batchelor to form spirals out of lampblack, Edison and his staff began to consider alternative ways to make carbon burners for the lamp using other substances.  In the early morning hours of October 22 1879, they began what Charles Batchelor called "some very interesting experiments on straight carbons made from cotton thread so.  We took a piece of 6 cord thread No 24 which is about 13 thousandths in thickness and after fastening to Pt wires we carbonized it in a closed chamber.  We put bulb in vacuo and it gave a light equal to about 1/2 candle 18 cells carbon [battery], it had resistance of 113 ohms at starting and & afterwards went up to 140--probably due to vibration."

After the lamp had been left burning for 13 1/2 hours, they added enough battery cells to increase its light to the equivalent of three gas jets (at least 30 candles).  Although this caused the bulb to overheat and crack after another hour, the laboratory staff had for the first time produced a lamp that showed true commercial promise.

In the weeks following the first carbon thread lamp experiments, the laboratory staff tried nearly every carbon substance readily available in the laboratory.  A list of twenty items carbonized by Batchelor on October 27 suggests the range of materials they investigated--a variety of woods and papers, vulcanized fibre, celluloid, cotton lampwick, flax, cork, cocoa nut hair and shell, and fishing line.  The optimism produced by the carbon breakthrough was apparent in Francis Upton's letter home on November 2:

"The electric light is coming up.  We have had a fine burner made of a piece of carbonized thread which gave a light of two or three gas jets.  Mr. Edison now proposes to give an exhibition of some lamps in actual operation.  There is some talk if he can show a number of lamps of organizing a large company with three or five millions capital to push the matter through.  I have been offered $1,000 for five shares of my stock. . . . Edison says the stock is worth a thousand dollars a share or more, yet he is always sanguine and his valuations are on his hopes more than his realities. "

Although the carbonized thread showed promise, the difficulties of producing a commercial carbon lamp were becoming apparent and Upton confessed the following week, "The Electric Light seems to be a continued trouble for as yet we cannot make what we want and see the untold millions roll upon Menlo Park that my hopes want to see."  By November 16, however, they had "the first lamp that answers the purpose we have wished.  It is cheap much more so than we even hoped to have. "The lamp is obtained from a piece of charred paper which is bent thus [into a horseshoe shape].  The burner is made from common card board and cut to about the size shown [1" high].  This is then sealed  in a glass bulb  and the air exhausted and then a current of electricity passed through it which heats it to a brilliant whiteness so that it will give a light equal to that from a good sized gas burner."

Demonstrating the New Light
Edison quickly moved forward with his plans to publicly exhibit the light and gave John Kruesi the task of overseeing the preparations, which he detailed in an order book.  Edison’s staff wired the laboratory complex, houses, and other buildings at Menlo Park and set up a line of poles with lamps to light the streets, all connected with a generator located in the machine shop. Reports of the successful demonstration for the Electric Light Company investors on December 27 brought large crowds of curiosity-seekers to see the new system as it was exhibited during the New Year holiday. 

On December 30, according to the New York Herald, "Menlo Park [was] thronged with visitors coming from all directions to see the `wonderful' electric light.  Nearly every train that stopped brought delegations of sightseers until the depot was overrun and the narrow plank road leading to the laboratory became alive with people.  In the laboratory the throngs practically took possession of everything in their eager curiosity to learn about the great invention."  Somehow amidst all the confusion final preparations were finished for the public demonstration the following day. 

The Herald described another enthusiastic crowd for the New Year's Eve demonstration:

Extra trains were run from east and west, and notwithstanding the stormy weather, hundreds of persons availed themselves of the privilege.  The laboratory was brilliantly illuminated with twenty-five lamps, the office and counting room with eight, and twenty others were distributed in the street leading to the depot and in some of the adjoining houses.  The entire system was explained in detail by Edison and his assistants, and the light was subjected top a variety of tests.

The front page of the New York Daily Graphic depicted the demonstrations.

The following day the large crowds again came to the laboratory where they "went pellmell through the places previously kept sacredly private."  By the end of the day, the Herald reported, Edison felt compelled to order the laboratory closed to the general public, "directing, however, that the private dwelling in Menlo Park, as well as the street lamps, be kept burning nightly, so that those who come will not be disappointed."

Edison had to close the laboratory to visitors in order to continue work on the lighting system.  He understood better than anyone that he had only demonstrated that it worked on a small, experimental scale.  Bringing the system into commercial operation would require an intensive effort to refine each part of the system to make it reliable in public use.  Perhaps even more importantly, he recognized that he would only succeed if he could successfully compete economically with gaslighting. 

From Research to Development
From the very beginning of his research Edison had periodically considered other elements of his system, such as meters and underground conductors, but the during the research phase he and his staff had focused on the lamp and generator.  With the shift to commercial development, they now paid greater attention to the rest of the system.  With an expanded staff Edison was able to assign the development of these minor though important components to his assistants. Nonetheless, the lamp remained the most important subject of research during 1880 as Edison sought a commercial lamp capable of hundreds of hours of use. 

Lamp research focused on each part from the filament to the electrical connections to the glass bulb.  Most of the experiments, however, were designed to find the best filament material for the commercial lamp. The lamps used during the New Year demonstrations were made with carbonized cardboard filaments in the shape of a horseshoe.  While cardboard worked for a demonstration, it had serious defects that made it impractical for use in a commercial lamp.  As one of his assistants later recounted, Edison discovered that "Paper is no good.  Under the microscope it appears like a lot of sticks thrown together.  There are places where the fibres are packed and other places where there are few fibres, dense spots and great open holes."  If carbon was the solution, he still needed to find the best form of it.  In typical Edisonian fashion he told his staff, "Now I believe that somewhere in God Almighty's workshop there is a vegetable growth with geometrically parallel fibres suitable to our use.  Look for it.  Paper is man made and not good for filaments."  Edison assigned one of his chemists, Dr. Otto Moses, to make a systematic study of scientific literature on carbon substances which helped to guide the research.  Filament experiments soon focused on grasses and canes such as hemp, palmetto, and bamboo which possessed long, uniform fibers that would make for a sturdy long-lasting filament. By July 1880, bamboo and bast had become the most promising materials and by the beginning of December Edison finally settled on bamboo as the best material for the commercial lamp.

During the spring and summer the staff was busy building a full-scale model of his underground system at Menlo Park.  This system would allow him to test each component and also provide more exact knowledge regarding costs. The installation of the Menlo Park system provided the impetus for work on many of the components to be used in a commercial system, which Edison had put aside while focusing on the dynamo and lamp. During this period the staff worked on a variety of components, including meters, fuses, sockets and fixtures. The underground system required a good insulation for the wires, and he placed Wilson Howell in charge of devising an insulating compound

By the late spring of 1880, Edison also began to consider the problems of lamp manufacture as he made plans to convert the old electric pen factory at Menlo Park into a lamp factory.  Although technical problems remained, Edison wanted to work out some of the manufacturing difficulties and to make large test runs of experimental lamps. During the summer he had his experimenters and machinists design special tools for making filaments, clamps, and bulbs.  The most important work focused on improved vacuum pump designs intended to reduce the time required to evacuate a lamp.  By the end of September the factory was producing experimental runs of bulbs.  At the end of December Francis Upton was placed in charge of the factory and regular production finally began in March or April 1881.

As he began to make plans for a large central station in New York, Edison designed a new steam dynamo to reduce the energy lost in the linkage between engine and generator.  Developed with steam engine maker Charles T. Porter, this was a 100-horsepower generator coupled directly to a high-speed steam engine that would waste less energy than using several smaller dynamos run from an engine with belts and pulleys. Charles Clarke, a mechanical engineer who had been Upton's classmate at Bowdoin College, was given the job of supervising the construction and testing of this dynamo.  This design came to be known as the "Jumbo," after the famous elephant exhibited by P. T. Barnum at Madison Square Garden in April 1882. 

Edison also had to convince the New York City Board of Aldermen to approve the laying of underground conductors for the station. He invited the Aldermen to come to the laboratory on Monday evening, December 20.  A reporter from Truth described the effect of the demonstration and the lobbying effort:

By this time the city fathers had begun to look quite dry and hungry, and as though refreshments would have looked much more palatable to them than the very scientific display they had been wondering at for two hours without a great deal of comprehension, although with a wonderful exhibition of understanding and appreciation.

Their hopes were quickly realized by the announcement that the collation was ready. For half an hour only the clatter of dishes and the popping of champagne corks could be heard, and then the wine began to work and the Aldermen, true to their political instincts, began to howl, "Speech, speech." One of the witnesses of this visit said that the City Fathers were amazed at the appearance of the man they called "Professor" Edison. "Why," whispered one City Father to another, "he looks like a regular fellow. See how he handles his cigar—just like the boys in the Wigwam [Tammany Hall]."

More negotiations followed to work out the terms under which Edison interests would be allowed to dig up the streets, but the demonstration at Menlo Park left no doubt of the workability of the Edison system.

Menlo Park Lab Menlo Park shop Menlo Park upstairs
Dynamo Room, Pearl Street Station Pearl Street Station cross section Map showing area lighted by Pearl St.

In March 1881, Edison moved his operations from Menlo Park to New York, where he expanded his manufacturing operations with three additional factories: the Edison Machine Works, which manufactured dynamos; the Electric Tube Company, which manufactured insulated underground condcutors; and Bergmann & Company, which manufactured most of the other small elements of the system.  Edison’s own time was largely spent overseeing the installation of the large central station plant on Pearl Street in lower Manhattan, which finally commenced operation on 4 September 1882, almost four years to the day after Edison began experimenting on the electric light.

On the occasion of the 35th anniversary of the electric light Edison offered a prediction that foreshadows its impact on the modern world. 

“The one great value of the electric light – and the electric railway too – is that they expand mankind’s day. . . In the old days man went up and down with the sun.  A million years from now we won't go to bed at all.  Really, sleep is an absurdity, a bad habit.  We can't  suddenly throw off the thraldom of the habit, but we shall throw it off." 

Want to know more about the Menlo Park laboratory? Check out The Invention Factory.

Suggested reading: Edison's Electric Light by Robert Friedel and Paul Israel