In physics, the Rayleigh-Jeans Law, first proposed in the 19th century, expresses the energy density of blackbody radiation of wavelength λ as

<math> f(\lambda) = 8\pi k\frac{T}{\lambda^4}<math>

where λ is in meters, T is the temperature in Kelvins, and k is Boltzmann's constant.

The law agrees with experimental measurements for long wavelengths but disagrees for short wavelengths, where it diverges and leads to the ultraviolet catastrophe.

Max Planck revised the law to state:

<math>f(\lambda) = \frac{8\pi hc}{\lambda^5}~\frac{1}{e^\frac{hc}{\lambda kT}-1}<math>

where h is Planck's constant, c is the speed of light. This is Planck's law of black body radiation expressed in terms of wavelength λ=c/ν. It can be seen that for high temperatures or long wavelengths, the term in the exponential becomes small, and so the term in the denominator becomes approximately hc/λkT which gives back the Rayleigh-Jeans Law.

See also

• John William Strutt, 3rd Baron Rayleigh