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). For the greatest accuracy, the spectrum must be recorded on an instrument that is corrected for the wavelength-dependence of the detector sensitivity.

**Download links:**

Download spreadsheet in Excel
format (.xls)

Download spreadsheet in
OpenOffice format (.ods)

WingZ version: black.wkz; Screen image.

Wingz player application and basic set of simulation modules,
for windows PCs or Macintosh

Other simulations that
employ a blackbody source:

Signal-to-Noise
Ratio of Absorption Spectrophotometry

Fluorescence
Spectroscopy Signal-to-Noise Ratio

U.V.-Visible
Spectrophotometer

Dual
Wavelength Spectrophotometer

**Note**: It is also possible to use the more
advanced technique of iterative
least-squares curve fitting to *automatically *adjust
the parameters of the blackbody
equation to
fit the measured spectrum of an incandescent body for the
purpose of estimating its color temperature and emissivity. The Matlab/Octave
script BlackbodyDataFit.m demonstrates
the technique, placing the experimentally measured spectrum in
the vectors "wavelength" and "radiance" and then calling the
built-in minimum finder function *fminsearch
*with the fitting function fitblackbody.m.

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

Computes the spectral radiance, total radiance, and peak wavelength of a blackbody source, given the temperature and emissivity. Also plots spectral radiance vs wavelength from 150 nm to 3500 nm.

Note: to run the OpenOffice
(.ods) spreadsheets, you have to first download the OpenOffice
installer (download
from OpenOffice), then install it (by double-clicking on the
installer file that you just downloaded), and then download my
spreadsheets from this page. Once OpenOffice is installed,
you can run my spreadsheets just by double-clicking on them.

(c) 1991, 2015. This page is part of Interactive Computer Models for Analytical Chemistry Instruction, created and maintained by Prof. Tom O'Haver , Professor Emeritus, The University of Maryland at College Park. Comments, suggestions and questions should be directed to Prof. O'Haver at toh@umd.edu.

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