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What is the First Radiation Constant?

Black body radiation intensity vs. wavelength

The first radiation constant, c1, is used in 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 = c1-5 / (εc2/λT - 1)

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