LumaSense Technologies MC320 Manual - Manual (Page 20)

20 Principle of Thermal Imaging MC320 Thermal Imager Manual
4.2 Emissivity
Infrared radiation is energy radiated by the motion of atoms and
molecules on the surface of object, where the temperature of the
object is more than absolute zero. The intensity of the emittance
is a function of the temperature of the material. In other words,
the higher the temperature, the greater the intensity of infrared
energy that is emitted. As well as emitting infrared energy,
materials also reflect infrared, absorb infrared and, in some cases,
transmit infrared. When the temperature of the material equals
that of its surroundings, the amount of thermal radiation
absorbed by the object equals the amount emitted by the object.
Transmission,
Absorption, and
Reflection of Infrared
Energy
The figure above shows the three modes by which the radiant
energy striking an object may be dissipated. These modes of
dissipation are:
a = absorption
t = transmission
r = reflection
The fractions of the total radiant energy, which are associated
with each of the above modes of dissipation, are referred to as
the absorptivity (a) transmissivity (t) and the reflectivity (r) of the
body. According to the theory of conservation of energy, the
extent to which materials reflect, absorb and transmit IR energy is
known as the emissivity of the material.
4.3 Blackbody Radiation
The emissivity of a body is defined formally by the equation
below as the ratio of the radiant energy emitted by the body to
the radiation, which would be emitted by a blackbody at the
same temperature.