property>first radiation constant
What is the First Radiation Constant?
![Black body radiation intensity vs. wavelength Black body radiation intensity vs. wavelength](/images/properties/first_radiation_constant.jpg)
The first radiation constant, c1, is used in the Planck's law. It has the SI units of watts square metres. It is given by the equation:
c1 = 2π.hc2
where h is the Planck constant and c is the speed of light. Its value is 3.741771x10-16 Wm2.
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)