Blackbody radiation is produced by any source with a temperature above absolute zero, which is everything. The light given off by this source is governed by two important laws. The first of these is referred to as Wien's law. Wien's law states that the peak wavelength of light from a thermal source is inversely proportional to the absolute temperature of the source. That is to say, the higher the temperature the shorter the wavelength, or the higher the temperature the bluer the color.

The second of these laws is referred to as the Stefan-Boltzmann law. The Stefan Boltzmann law states the higher the temperature the more light is being given off. In fact, the amount of energy given off by the light is proportional to the absolute temperature to the fourth power. This means that a small change in temperature yields a large change in energy given off. The amount of energy given off is the same as the brightness of the object.

The diagram below graphically represents both of these laws. Notice, that as the temperature increases (the temperature is increasing from front to back) the top of the graphical hill moves to the left which is towards smaller wavelength. Also note, that as the temperature increases the height of the hill also increases.

The following link will take you to web pages with java applets showing how the spectra changes with changing temperature. These applets require a web navigator capable of running Java 1.1. Netscape Communicator 4.5 and higher and Internet Explorer 5 and higher are examples of Java capable browsers. Make sure your computer is capable of handling these browsers before loading them. If you move to these pages without the proper browser, the applet will not function. You will not crash your system. Just click back to return to this page.

Blackbody Exercise

This page was last updated on 06/13/01.