LumaSense Technologies BoilerSpection-SD - Manual (Page 46)

BoilerSpection HD/SD Manual Principles of Thermal Imaging 46
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In radiation of a normal object, as the emissivity is (<1) times of the blackbody, multiply above
equation by the emissivity. The following figures show the spectral radiant emittance of a
blackbody.
(a) is shown by logarithmic scale and (b) is shown by linear scale.
Figure 30: Spectral radiant emittance of a blackbody
6.4 Blackbody Type Source and Emissivity
Although a blackbody is actually only a theoretical ideal, an object can
be manufactured which approximates it. A law closely related to the
blackbody is Kirchhoff’s law that defines reflection, transmission,
absorption and radiation.
a = e = 1
Absorptivity equals emissivity, thus emissivity can be described by
reflectivity and transmissivity.
e + t + r = 1
Key:
a = absorptivity
t = transmissivity
r = reflectivity
e = emissivity