How is light formed in a light bulb?

Asked by: Erika

Answer

There are several types of light bulbs and they emit light through different mechanisms. I'll try to explain how incandescent light bulbs work.

A regular incandescent light bulb relies on the fact that all bodies with a temperature greater than absolute zero emit radiation. This radiation is logically named thermal radiation and the intensity of radiation emitted at a given wavelength is a function of the temperature of the body. At low temperatures a body emits very low intensity radiation, mostly of lower energy than visible light. The visible light that is emitted is of far to low intensity to be seen by human eyes. However at high temperature the intensity of visible light (and other radiation) emitted by the body increases. Depending on its specific physical properties a body may emit more or less visible light at a given temperature. Incandescent light bulbs use a thin wire called a filament (traditionally made of tungsten, perhaps currently made of a different material) as a thermal radiation emitting body. The filament has a very tiny axial diameter (it is skinny) and therefor a fairly high resistance to current. When AC current flows through the filament it is heated very rapidly to a very high temperatures (that is why incandescent light bulbs are hot) and it emits lots of thermal radiation in the visible spectrum.
Answered by: Ed Nicholas, M.S., Medical Science Grad. Student