Tuesday, May 15, 2001

How Does a Lightbulb Work?

A light bulb is made from a very thin piece of glass. The glass is heated up and blown into a shape of a bulb. Once cooled, the inside of the bulb is coated with a material that diffuses the light. The filament of a light bulb is made of tungsten. Tungsten is a metal like element that burns in the presence of oxygen. The tungsten wire that the filament is made from is very thin, on the order of 0.0017 inches thick! The filament is made of coiling the tungsten wire around itself, forming a double coil. The ends of the coil are then attached to power leads that are inside the glass base of the bulb. The glass top and bottom are then melted together, the bulb is sealed, and the oxygen is removed from the bulb. Various gases can then be introduced into the bulb. A metal base is added and the bulb is ready to use.

In a normal light bulb an electric current travels through a coiled tungsten wire. Current is carried in a wire by bumping electrons off of the atoms or molecules that make up the wire, like marbles. One electron is bumped which bumps another electron. Electrons do not collect within the wire, but rather one electron is bumped and replaced in the atom by the one that bumped it. This bumping creates energy. The energy is released as heat in the filament and can heat the filament to up to 2500 degrees Celsius! At 2500 degrees Celsius the light bulb emits about 12% of its energy as visible light. Energy is also given off from the bulb as invisible infrared light or heat.

Evidence exists that Thomas Edison was not actually the inventor of the light bulb. In 1878 British inventor Joseph Swan patented the carbon filament light bulb. That following year Edison patented the same carbon filament bulb. As a result of the law suit Swan flied against Edison, the Edison and Swan Electric Company was formed. In 1882 Swan sold his patent to Brush Electric Company. Edison owned Brush, later General Electric, and got the credit for the patents. The light bulb developed by Swan and Edison is based on the same principles as the ones we currently use today. Improvements in the make up of the filaments have been made to lengthen the life of the bulb.

In neon lights, similar concepts are used. Different gases and coatings can be added to the glass to induce different colors.