# property>first radiation constant

## What is the First Radiation Constant?

The first radiation constant, c_{1}, is used in the Planck's law. It has the SI units of watts square metres. It is given by the equation:

c_{1} = 2π.hc^{2}

where h is the Planck constant and c is the speed of light. Its value is 3.741771x10^{-16} Wm^{2}.

Planck's law gives the radiation intensity emitted by a black body for a given frequency and temperature. It has the form:

u = c_{1}.λ^{-5} / (ε^{c2/λT} - 1)