Download WienÕs Law

Wien’s Law
Wien’s Law, sometimes called Wien’s Displacement Law, predicts the temperature of a
blackbody from the wavelength of its peak emission. As with all laws about light, the
wavelength need not be visible.
The form of Wien’s Law is inverse; the longer the wavelength of light of the peak
emission, the cooler the temperature of the emitting body. Note that this is surface
temperature, not the interior temperature of a star or planet which may be much higher.
Wien’s Law is written:
𝑇 = 2.4 × 10!
𝜆
where T is the temperature of the blackbody in Kelvins (K) and λ is the wavelength of its
peak emission in nanometers (nm).
As an example, the Sun has a peak of emission in the green portion of the visible
spectrum, which is about 550 nm. Plugging this into the equation yields a temperature of
the solar surface of 6000 K.
Similarly, the Earth has a peak of emission in the infrared portion of the electromagnetic
spectrum at 10,000 nm. This yields a temperature of 300 K, which is 27° C (roughly
room temperature).