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18 – Theory of thermography
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Figure 18.5 Wilhelm Wien (1864–1928)
The sun (approx. 6 000 K) emits yellow light, peaking at about 0.5 μm in the middle
of the visible light spectrum.
At room temperature (300 K) the peak of radiant emittance lies at 9.7 μm, in the far
infrared, while at the temperature of liquid nitrogen (77 K) the maximum of the almost
insignificant amount of radiant emittance occurs at 38 μm, in the extreme infrared
wavelengths.
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Figure 18.6 Planckian curves plotted on semi-log scales from 100 K to 1000 K. The dotted line represents
the locus of maximum radiant emittance at each temperature as described by Wien's displacement law.
2
1: Spectral radiant emittance (W/cm
(μm)); 2: Wavelength (μm).
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Publ. No. 1558146 Rev. a156 – ENGLISH (EN) – February 28, 2006
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