PHY 212 Net Research Project for 2/2/04

Edison and the Incandescent Light Bulb

Thomas Edison is probably the best known American inventor/scientist. He began at a very early age experimenting with voltaic cells (early batteries) in his parent's basement. Edison's first patented invention (1868) was the Electrical Vote Recorder. He tried to sell it to Congress, but they were not interested in counting votes quickly. (As the country grew, the voting machine became inevitable.) The legend goes that Edison vowed he would never again invent anything unless there was a commercial demand for it.

He set up his first laboratory dedicated to this premise in 1869 with $40,000 paid to him by the Gold and Stock Telegraph Co. Apparently the telegraph device used at that time was notoriously unreliable. Edison invented the very reliable Universal Stock Ticker and wanted $5000 for it ... but the GST Co offered the 40k before Edison spoke. He swallowed his words and said that that seemed fair.

Edison's list of inventions is quite astounding. Over a period of about 65 years, he was awarded 1093 patents. This fact supports the reputation he had as being a tough task master at his laboratory! But it was in 1878 that he produced what was probably his most important invention; a viable incandescent light bulb. He spent many years perfecting it.

Up until that time, the open-air carbon arc lamp was the only electrical source of light. This device operated at temperatures high enough to melt carbon rods. It was impressive, but big, dangerous (the carbon arc was not enclosed) and expensive. The new incandescent technology provided a small and inexpensive source of light at relatiely low voltages. (Carbon arc lamps are still manufactured for use in search lights, theaters and the film industry.)

Today there is a great variety of light bulbs available. But they fall into two broad categories; the incandescent light, in which a filament is heated to glowing temperatures, and the vapor light, in which light is emitted from a hot vapor. Peter Hewitt is credited with inventing the first enclosed vapor light in 1934. He used mercury (Hg) for the vapor, a source still use today for many street lights. The flourescent lights that you find all over campus are vapor technology lights. You can get more info on both types from bicycle-light enthusiast Marty Goodman on his history of lighting technology page.

Besides cost and efficiency, there is another significant difference between the two technologies. The incandescent light produces a continuous visible spectrum that is very similiar to that of the light from the sun. (The spectrum refers to the range of colors in the light. We will study the spectrum is greater detail in the coming weeks.) Vapor lights generally have gaps in the spectrum and some produce higher intensity in the potentially problematic ultraviolet (UV) region. Most people prefer incandescent light, claiming that the quality of light is better than that from vapor lamps. Is there any reason other than appearance to be concerned about the spectrum?

There are several concerns about the spectrum of lights. It has long been known that many plants do not repond as well to flourescent lights as to "full spectrum" light. Although there are a few vapor-technology lights that claim to provide a good approximation, incandescent lights are still the predominant choice for plant lovers.

There is concern about the effect on humans and animals, as well. Several studies on the effects of light on school children have demonstrated that students perform better under natural sunlight. The psychology profession has long recognized the importance of light to humans and its relationship to SAD (seasonal affective disorder). It is not yet clear whether the effects are due to the spectrum profile, intensity, length of exposure, or some combination of all these factors. Dr. Norman Rosenthal is one of the many psychiatrists working on SAD research. Here is a short description of his findings on the relationship between full spectrum lighting and SAD.

Be sure to enter your full name. Enter your email address ONLY if you want the number of points awarded e-mailed to you. Responses should be brief but complete. You must click the SUBMIT button to submit your entry. Entries are due by noon on Monday of next week.