[9.4 — Infrared semi-transparent materials]
© FLIR Systems AB – Publ. No. 557 369 – Ed. A
57
This states that the total emissive power of a greybody is the same as a blackbody
at the same temperature reduced in proportion to the value of e from the grey-
body.
Figure 9:4 Spectral radiant emittance and spectral emissivity of three types of radiators.
9.4 Infrared semi-transparent materials
Consider now a non-metallic, semi-transparent body – let us say, in the form of a
thick flat plate of plastic material. When the plate is heated, radiation generated
within its volume must work its way toward the surfaces through the material in
which it is partially absorbed. Moreover, when it arrives at the surface, some of it is
reflected back into the interior. The back-reflected radiation is again partially
absorbed, but some of it arrives at the other surface, through which most of it
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