Who invented the electric bulb? A majority of people would reply ‘Thomas Edison’. But the majority need not be always right. Even before Thomas Alva Edison started working on it, many inventors had already developed various forms of electric bulbs.

Historically the credit goes to Sir Humpry Davy, a British chemist. As early as in 1809, he connected two wires to a large battery and attached a charcoal strip between the ends of the wires. The charged charcoal glowed, creating the first ‘arc lamp’. However, the light from arc lamps was too harsh and unfit for home use. They were useful for large area illumination such as street lighting, sports fields etc. The present day mercury lamps, sodium lamps, metal halide lamps, etc are the advanced avatars of Davy’s arc lamp.

By 1870 inventors in both Europe and North America were racing to develop a light bulb for home use, by the principle of incandescence. Electric current passing through a filament heats it up. The heat excites the atoms in the filament to emit light. Though the principle is simple, there were two main hurdles in putting it to practice. First, visible light will be emitted only when the filament is heated to very high temperatures making it ‘white hot’. There were very few materials which could withstand such temperatures without melting. The second problem was when the filament was heated it combined with oxygen in the air and caught fire.

Wires of metal such as platinum were considered for the filament. However, its low melting point (1775 degree Celsius), low electrical resistance, high current draw and high cost prevented its effective use in incandescent lamps. The inventors then turned to carbon which had the required properties like high melting point, high electrical resistance and less expensive. They experimented with various forms of carbonized filaments.
The second problem was largely solved by the 1870s with the invention of vacuum pumps.

The inventors could enclose the filament in a glass bulb, evacuate it to remove air and oxygen to prevent it from catching fire.

‘Swan’ song!
The most successful among the inventors of that time was Joseph Wilson Swan, an English Physicist. In 1878 he developed an evacuated bulb with carbon filament which lasted as long as 13.5 hours. Swan further improved his invention, obtained a patent and gave the world’s first large-scale public exhibition of electric lamps in New Castle, England in the 1880s. He even established a company for installing light bulbs in homes and public places.
Around the same time two Canadians— Harry Woodward and Mathew Evans, built electric bulbs of different sizes and shapes with carbon filaments and patented them.

So when Thomas Ala Edison started work on electric bulb in the mid 1870, already a number of inventors were on the job. After some initial unsuccessful experiments Edison found that Woodward and Evans approach was very useful, bought their patents and started improving them. With better vacuum and improvised carbonized filaments he was able to extend the life span of the bulb from 13 hrs to 40 hrs, 600 hrs and finally 1200 hrs. He also obtained a US patent for ‘Electric Lights’ in 1880.

Though Edison’s lamp lasted long enough for home use, it had problems. It gave out only yellow light and very low in brightness— only about 3.5 lumens per watt. Even though carbon had a high melting point, at high temperatures it evaporated coating the inner surface of the bulb, further reducing the light output.
The next big invention was in 1910 by William Coolidge, a school drop out. He developed, for the General Electric Company, filaments from tungsten which has a high melting point (2,750 degree Celsius) in a cost-effective manner. He also filled the bulb with an inert gas like nitrogen to give it structural stability. His bulbs gave white light with an output of 10 to 12 lumens per watt, similar to the present day bulbs.

Complete package
It is true that Edison invented an electric bulb. But he was neither the first nor the only one. There were in all at least 27 inventors of incandescent bulbs and several patents. So it is reasonable to ask why Edison got the entire credit while others like Joseph Swan, Harry Woodward and Mathew Evans were ignored.

According to science historians Robert Friedel and Paul Israel, Edison’s version prevailed because of its much longer filament life (before the tungsten lamps came on). More importantly, unlike others who concentrated only on the bulb, Edison developed the entire electric lighting system, complete with an electric generator, distributor and wiring arrangement to take the electric lamp to the homes of common man. The lamp was only a small component of his system.

Brilliant Tesla!
However, even here he was soon overcome by another brilliant inventor Nikola Tesla. Edison’s lighting system was based on a direct current (DC) generator. In fact Tesla worked for Edison for some time and even improved his DC generator. Later they parted and Tesla established his own company to produce the much superior alternating current (AC) generators.

It could transmit a larger amount of current at high voltage over much longer distances at a lower cost. In due course, Tesla’s AC generators replaced Edison’s DC generators, taking electricity to every nook and corner of the world.

It is thus a freak in the history of science that the credit for the invention of electric bulb went only to Edison. There are many such instances. The credit for the invention of radio is even more bizarre, with one of the famous Indian scientists playing a seminal role in its development. But that story later!