Color Temperature of a Blackbody Source

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Evaluation of the Planck blackbody equation. Demonstrates how the emission spectrum of a blackbody radiator depends on its temperature and emissivity.

This model can be used to determine whether a light source has a blackbody-like emission spectrum and to estimate its temperature and emissivity if so. Students take experimental measurements of the radiance of a light source at various wavelengths, type in the values of wavelength and radiance into the table on the right, then adjust the parameters of the model (temperature and emissivity) so that the calculated blackbody spectrum (shown by the red line) is a best fit to the experimental data points (shown by the blue dots).

Download link: black.wkz;
Wingz player application and basic set of simulation modules, for windows PCs or Macintosh

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Mathematical basis

Blackbody temperature, T (in degrees K), set by on-screen slider.
Emissivity, set by on-screen slider.
Calculated radiance = emissivity*1.19111E+16*wavelength^(-5)/(exp(14380000/(wavelength*T))-1)
The graph shows a plot of calculated radiance (red line) and measured radiance (blue dots) 
vs wavelength