colour.colorimetry.blackbody_spectral_radiance(wavelength, temperature, c1=3.741771e-16, c2=0.014388, n=1)

Returns the spectral radiance of a blackbody at thermodynamic temperature \(T[K]\) in a medium having index of refraction \(n\).

  • wavelength (numeric or array_like) – Wavelength in meters.

  • temperature (numeric or array_like) – Temperature \(T[K]\) in kelvin degrees.

  • c1 (numeric or array_like, optional) – The official value of \(c1\) is provided by the Committee on Data for Science and Technology (CODATA) and is \(c1=3,741771x10.16\ W/m_2\) (Mohr and Taylor, 2000).

  • c2 (numeric or array_like, optional) – Since \(T\) is measured on the International Temperature Scale, the value of \(c2\) used in colorimetry should follow that adopted in the current International Temperature Scale (ITS-90) (Preston-Thomas, 1990; Mielenz et aI., 1991), namely \(c2=1,4388x10.2\ m/K\).

  • n (numeric or array_like, optional) – Medium index of refraction. For dry air at 15C and 101 325 Pa, containing 0,03 percent by volume of carbon dioxide, it is approximately 1,00028 throughout the visible region although CIE 15:2004 recommends using \(n=1\).


Radiance in watts per steradian per square metre.

Return type

numeric or ndarray


  • The following form implementation is expressed in term of wavelength.

  • The SI unit of radiance is watts per steradian per square metre.




>>> # Doctests ellipsis for Python 2.x compatibility.
>>> planck_law(500 * 1e-9, 5500)