Planck's Law - FLIR Ex series User Manual

18 Theory of thermography

18.3.1 Planck's law

Figure 18.3 Max Planck (1858–1947)
Max Planck (1858–1947) was able to describe the spectral distribution of the radiation
from a blackbody by means of the following formula:
where:
W
λb
c
h
k
T
λ
Note The factor 10 -6 is used since spectral emittance in the curves is expressed in Watt/
m 2 , μm.
Planck's formula, when plotted graphically for various temperatures, produces a family of
curves. Following any particular Planck curve, the spectral emittance is zero at λ = 0, then
increases rapidly to a maximum at a wavelength λ
again at very long wavelengths. The higher the temperature, the shorter the wavelength at
which maximum occurs.
#T559828; r. AK/40423/40448; en-US
Blackbody spectral radiant emittance at wavelength λ.
Velocity of light = 3 × 10 8 m/s
Planck's constant = 6.6 × 10 -34 Joule sec.
Boltzmann's constant = 1.4 × 10 -23
Absolute temperature (K) of a blackbody.
Wavelength (μm).
and after passing it approaches zero
max
Joule/K.
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