15
Emissivity and IR Measurement Theory
IR Thermometers measure the surface temperature of an object.
The thermometer’s optics sense emitted, reflected, and
transmitted energy. The thermometer’s electronics translate the
information into a temperature reading which is then displayed
on the LCD.
The amount of IR energy emitted by an object is proportional to
an object's temperature and its ability to emit energy. This ability
is known as emissivity and is based upon the material of the
object and its surface finish. Emissivity values range from 0.1 for
a very reflective object to 1.00 for a flat black finish. For the
Model 81998, the emissivity is adjustable from 0.1 to 1.00. Most
organic materials and painted or oxidized surfaces have an
emissivity factor of 0.95. When in doubt, set the emissivity to
0.95.
Emissivity Factors for Common Materials
Material Emissivity Material
Emissivity
Asphalt
0.90 to 0.98
Cloth (black)
0.98
Concrete 0.94
Skin
(human)
0.98
Cement 0.96
Leather
0.75
to
0.80
Sand 0.90
Charcoal
(powder)
0.96
Soil
0.92 to 0.96
Lacquer
0.80 to 0.95
Water
0.92 to 0.96
Lacquer (matt)
0.97
Ice
0.96 to 0.98
Rubber (black)
0.94
Snow 0.83
Plastic
0.85
to
0.95
Glass 0.90
to
0.95
Timber
0.90
Ceramic 0.90
to
0.94 Paper
0.70
to
0.94
Marble 0.94
Chromium
Oxides
0.81
Plaster
0.80 to 0.90
Copper Oxides
0.78
Mortar
0.89 to 0.91
Iron Oxides
0.78 to 0.82
Brick 0.93
to
0.96
Textiles
0.90
