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Electric Light Bulb

By zipjke May 06, 2013 1119 Words
Electric Light-Bulb

The modern world is an electrified world. The light bulb, which was probably one of the greatest inventions of all time, profoundly changed humans life by illuminating the night and making it hospitable to a wide range of human activity. Until the light bulb and electricity were invented, people could see at night only with candles, fires, gaslights, or oil lamps. The electric light bulb provided brighter light so people were better able to read, sew, and do other things that required a lot of light.

Electricity comes into a light bulb via a hot wire connected to a tab on the base of the bulb. Inside the bulb the electricity goes through a wire leading to a piece of tungsten. The tungsten is very thin and coiled to maximize resistance in the wire. When electricity meets resistance, it heats up the resistor.

The tungsten gets to a temperature of about 4500° Fahrenheit (2482° Celsius). This causes it to get white hot. It glows, and glows quite brightly. Tungsten is used because it has a very high melting point.

The tungsten is encased in a bulb for good reason. Not only does it protect people and objects from the hot tungsten, it also keeps oxygen away from the hot metal, which would make it immediately burn up. The bulb is usually filled with a low pressure, inert gas such as argon.

After the electricity has made its way through the tungsten filament, it goes down another wire and out of the bulb via the metal portion at the side of the socket. It goes into the fixture and out a white wire.

In the early 1800’s, inventors started experimenting with electric light. In 1802, Humphry Davy invented the first electric light. He experimented with electricity and created an electric battery. Then he used it to connect piece of carbon to it using wires, so that carbon glowed and produced light. His invention was known as the Electric Arc lamp. And while it produced light, it didn’t produce it for long and was much too bright for practical use.

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 3000oC / 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
Works Cited
“They All Laughed” by Ira Flatow, HarperCollins Publishers, 1992.

“The History of the Incandescent Lightbulb”. About.com Inventors. 12 May 2011. Mary Bellis 14 April 2013 http://inventors.about.com/library/inventors/bllight2.htm

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