property>second radiation constant
What is the Second Radiation Constant?
![illustration of a pyrometer from an early 20th century textbook illustration of a pyrometer from an early 20th century textbook](/images/properties/second_radiation_constant.jpg)
The second radiation constant, c2, is used in Planck's law. It has the SI units of metres kelvin. It is given by the equation:
c2 = hc / k
where h is the Planck constant, c is the speed of light and k is the Boltzmann constant. Its value is 1.438775x10-2 m K.
Planck's law gives the radiation intensity emitted by a black body for a given frequency and temperature. It has the form:
u = c1.λ-5 / (εc2/λT - 1)