English: There are a variety of ways of associating a characteristic wavelength or frequency with the Planck black-body emission spectrum. Each of these metrics scales similarly with temperature, a principle referred to as Wien's displacement law. For different versions of the law, the proportionality constant differs—so, for a given temperature, there is no unique characteristic wavelength or frequency.

The chart plots the peak of the Planck luminosity curve when it is plotted on a per wavelength basis ("peak wavelength"), on a per frequency basis ("peak frequency"), or on a per log(wavelength) or log(frequency) basis ("peak log wavelen. or freq."). Also plotted is the mean photon energy as a function of temperature, and the wavelengths at which 25% ("quartile"), 50% ("median"), or 75% ("quartile") of the black-body emissions have a lower wavelength. The "peak wavelength" curve nearly coincides with a quartile curve.

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Formulas for the various peak wavelengths and mean photon energy were taken from the Wikipedia Wien's displacement law page. The median and quartiles were computed by numerically integrating Planck's law; however, for any who wish to avoid this, information on percentiles is given in the Planck's law article.