The Story:

The invention of the incandescent light bulb has a history spanning from the early 1800s. Until that time, available light sources consisted of candles, oil lanterns, and gas lamps. In 1809, an English chemist, Humphrey Davy, started the journey to the invention of a practical incandescent light source. He used a high power battery to induce current between two charcoal strips. The current flowing through the two charcoal strips produced an intense incandescent light, creating the first arc lamp.

In 1820, Warren De la Rue made the first known attempt to produce an incandescent light bulb. He enclosed a platinum coil in an evacuated tube and passed an electric current through it. The design was based on the concept that the high melting point of platinum would allow it to operate at high temperatures and that the evacuated chamber would contain less gas particles to react with the platinum, improving its longevity. Although it was an efficient design, the cost of the platinum made it impractical for commercial use.

Throughout the 1800s, many scientists and inventors strove to create a cost effective, practical, long-life incandescent light bulb. The primary hurdle was creating a long-lived, high-temperature filament--the key to a practical incandescent light. Many high-melting-point materials were explored in inert/evacuated chambers in the process.

Men such as William Robert Grove, Frederik de Moleyns, W.E. Staite, John Daper, Edward G. Shepard, Heinrich Gobel, C. de Chagny, John T. Way, Alexander de Lodyguine, Joseph Wilson Swan, and Thomas A. Edison dedicated their time and efforts in the race to develop the first practical incandescent light bulb. Breakthroughs for Edison and Swan came in 1879, when they independently developed the first incandescent lamp that lasted a practical length of time -- at best a mere 13.5 hours. Their separate designs were based on a carbon fiber filament derived from cotton. The next stage of development focused on extending the practical life of the carbon filament bulb. Edison developed bamboo-derived filaments in 1880 that lasted up to 1200 hours.

The efficiency of an incandescent lamp design centers about attaining high filament temperatures without degradation and loss of heat. Edison’s early selection of carbon, the highest melting temperature element, with a melting point of 3,599^oC or 6510^oF seemed the obvious choice. The problem with carbon is that at high operating temperatures it evaporates, or sublimes, relatively quickly at 0.1 torr at 2,675^oC, resulting in short filament life.

The early solution to this dilemma was to operate the filament at lower temperatures to attain reasonable life. However, the incandescent brightness of the bulb was sacrificed in the process.

Other light bulb inventors tried two new filament materials to improve bulb brightness. In 1898, Karl Auer used osmium, which has a melting point of 2,700^oC / 4,890^oF. Then in 1903, Siemens and Halske worked with tantalum, which melts at 2,996 ^oC / 5,425^oF. These elements drew attention because they could operate at higher temperatures with longer life and less evaporation.

Then the invention of ductile tungsten, a much improved filament material, sparked the development of the modern tungsten filament incandescent light bulb by the General Electric Company and William Coolidge in 1906-10. This is the light bulb we know today. Ductile tungsten has many favorable properties such as:

• a high melting point: 3,410 ^oC / 6,170 ^oF
• low evaporation rate at high temperatures: 10^-4 torr at 2,757 ^oC / 4,995 ^oF
• tensile strength greater than steel

Because of its strength, ductility and workability, tungsten can readily be formed into the filament coils, used to enhance performance in modern incandescent bulbs. Due to its high melting point, tungsten can be heated to 3000^oC / 5,432^oF, where it glows white hot providing very good brightness. However, the early tungsten filaments still sublimed too quickly at such high temperatures. As they sublimed, they also coated the bulbs with a thin black tungsten film, reducing their light output.

Inert gases such as nitrogen and argon were later added to bulbs to reduce tungsten evaporation, or sublimation. While these gases reduced evaporation and increased filament life, they also carried heat away from the filament, reducing its temperature and brightness. Winding the wires into fine coils, as used in modern incandescent filaments, reduced convective heat loss, allowing the filament to operate at the desired temperatures.

Modern incandescent bulbs are not energy efficient, only four to six percent of the electrical power supplied to the bulb is converted into visible light. The remaining energy is lost as heat. However these inefficient light bulbs are still widely used today due to many advantages such as:

• wide, low-cost availability
• easy incorporation into electrical systems 
• adaptable for small systems
• low voltage operation, such as in battery powered devices
• wide shape and size availability