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 Infrared Theory
The Electromagnetic Spectrum
X rays, ultraviolet rays, visible light,
infrared energy, microwaves, and radio waves are all forms of
electromagnetic energy. Each category represents electromagnetic energy
within a specific range of wavelengths. Visible light,
for example, is electromagnetic energy with a wavelength between 0.4 and
0.75 micrometers (1µm = 0.001mm). Just as the unaided human eye is not
sensitive to X rays, ultraviolet rays, microwaves, and radio waves, the
eye is also not sensitive to infrared energy.
Infrared Energy
Each category of electromagnetic energy is
defined by a range of wavelengths. Infrared energy, for example, is
electromagnetic energy with wavelength from 1µm to 1000µm. OptoTherm
thermal imaging cameras are sensitive to a specific portion of the infrared
energy region with wavelength from 7 to 14µm, known as thermal infrared.
Temperature Defined
Temperature is a measure of an object’s
thermal energy. Thermal energy causes the atoms of a material to rotate
and vibrate and to radiate electromagnetic energy. The higher an object’s
temperature, the more its atoms rotate and vibrate, and the more energy it
emits. All objects with temperature above absolute zero have thermal energy
that can be radiated. Absolute zero is the temperature at which no
thermal energy exists in an object. It is impossible for any object to have
a temperature lower than absolute zero. Absolute zero is 0° on the
Kelvin scale, -273° on the Celsius scale and –459° on the Fahrenheit scale.
Thermal Imagers vs. Visible Light Cameras
It is important to understand the difference
in operation between thermal imagers and visible light cameras. Thermal
imagers detect infrared energy that is emitted (radiated) from objects.
Visible light cameras detect visible light that is reflected by objects.
Visible light cameras require visible light from an external source such as the
sun, a light bulb, or a flash bulb to illuminate and reflect off of an
object in order for its image to be captured. Thermal imagers and
infrared cameras require no
external infrared energy source in order to capture infrared images.
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