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 Episode 43 - Blackbodies: Play Now | Play in Popup | Download (105)

Example Blackbody Source - Image via Wikipedia

In this episode the topic of blackbody or thermal radiation is discussed. This is a connection between radiometry and photometry and temperature measurement. Discussed are blackbodies and what are called greybodies (blackbodies with emissivities < 0.99) Blackbody and greybody sources are used in the calibration of radiometric devices. The sun, stars, and the whole universe emit spectra consistent with a blackbody spectrum, as does every body at finite temperature. This is why one can measure temperature approximately by observing the electromagnetic radiation emitted from matter.

The spectral radiance (power radiated per unit area per unit solid angle per unit wavelength) of a blackbody is goverened by what is called Planck’s law:

This can be integrated to give the total radiant exitance (power radiated per unit area) F=σT⁴.

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