Every object that has a temperature (that is, every object in the Universe) gives off light at all wavelengths of the electromagnetic spectrum. But no object gives off all wavelengths equally: the Sun gives off more yellow light than radio waves, and a human body gives off more infrared radiation than x-rays. The wavelength at which an object gives off most of its light (often referred to as its "wavelength of maximum emission," its "lambda-max",or its "color") depends solely and entirely on its temperature, and can be computed using Wien's Law:

Notice the special units: wavelength is measured in Ångstroms, a unit of length where 1 Ångstrom = 10^-10 meters, and temperature is measured in Kelvins, a temperature system where water boils at 373 K, ice melts at 273 K, and 0 K is as cold as anything can get. To get temperatures in Kelvins, add 273 to the temperature in degrees Celsius.  If wavelength is to be measured in meters, the equation becomes

We shall see that this relationship between tempertaure and wavelength makes sense, since objects of higher temperature have more energy, and thus should give off photons of higher energy (lower wavelength).

Sample Calculations

To see some sample calculations with Wien's Law, click on the examples below

• Example 1
• Example 2

Updated 7/6/07

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