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BoilerSpection HD/SD Manual Principles of Thermal Imaging  46

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

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Lumasense-technologies BoilerSpection-SD Manual do Utilizador Página 46