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The **Planck function** is
a function of wavelength and temperature that
describes the spectral radiance at each wavelength in
black-body radiation.

- B(ν,T) - spectral radiance (specific intensity).
- ν - wavelength.
- h - Planck constant.
- T - temperature.
- c - speed of light.
- k
_{B}- Boltzmann constant.

2hν^{3}1 B(ν,T) = ———— ——————————— c^{2}e^{hν/(kBT)}- 1

Radiance is the quantity of radiation emitted through a surface into a given solid angle, spectral radiance being the radiance at a given wavelength.

black-body radiation