Trial Production of the World's First Double-Coil Bulb

Hakunetsu-sha (one of Toshiba's predecessors) was established in 1890 and started production of incandescent bulbs. However, making carbon filaments was extremely difficult back then. To create the bulb filament, the company first used cotton that had come with an English bulbmanufacturing machine the company had purchased from England, and then later followed Thomas Edison's example and tried bamboo. Since both materials had a high burnout rate, the company employed carbon filament made from cotton in 1900.

Having learned about the production of tungsten bulbs in the U.S. and Europe, Hakunetsu-sha began small-scale production of a prototype at its Mita main factory around 1907. The company later built a tungsten bulb production line and started full-scale production in 1910 at its newly constructed Kawasaki factory.

However, tungsten bulbs at the time used low-quality extruded-tungsten filament and productivity was low. The price of bulbs using this type of filament became quite high, and for a time the business was not profitable.

The news of William Coolidge's invention of drawn-wire tungsten filaments at the GE laboratories reached Japan in 1911. Hakunetsu-sha started production and sales of bulbs containing drawn-wire tungsten filament in October of the same year.

The invention of the ductile tungsten filament led to a fundamental improvement in material strength and uniform quality. It also had a revolutionary influence over the manufacturing of bulbs supported by the development of gas evacuation equipment for bulbs.

Irving Langmuir later discovered that the life of a bulb depended on the evaporation of tungsten from the filament. Thinking that the life of the filament could be extended by slowing the evaporation, in 1913 he invented a tungsten bulb filled with nitrogen gas, which is a substance that does not chemically combine with tungsten. Hearing the news, Hakunetsu-sha immediately imported and sold these bulbs in Japan and started making its own prototype.

A number of discoveries were made. Gas-filled bulbs were not so susceptible to blackening because less tungsten evaporated from the filament. A layer of gas is formed around the surface of the filament in an inert-gas environment–such as one using nitrogen–and a filament with a larger diameter loses less gas. Based on these facts, the effective diameter was made larger by converting a straight wire into a coil, and the assembly became known as a coiled-tungsten filament.

Engineers at Hakunetsu-sha conducted a great deal of research on the coiled-tungsten filament, particularly an engineer named Junichi Miura. Miura made the first prototype of the double-coil bulb in 1921. The double-coil bulb was more efficient than the single-coil bulb and people's expectations for the product were high. However, technology to mass-produce these bulbs was not yet available, and they were not put into practical use.

Hakunetsu-sha continued its research into tungsten filaments, gas-filled bulbs, and experimental double-coil bulbs. In 1930, the company adopted the product as a special bulb for kinetoscopes. It later created a technique to mass-produce double-coil bulbs that had the same level of uniformity as conventional gas-filled bulbs. They were launched as the new Mazda lamp–a gas-filled double-coil bulb–in 1936.

Tungsten bulb during Dr. Coolidge's period

Gas-filled light bulb invented by Dr. Langmuir

Brochure for the new Mazda lamp

Related Links

Learn (History/Science) Top Page