Infrared is a kind of
electromagnetic waves in the waveband between visible
light and
microwaves. It is called visible light if it is in the
range of 0.38~0.77μm, which
is visible to the naked eyes. Infrared is in the range
of 0.77~1,000μm, longer than the wavelength of visible
light, and it’s classified into ‘near infrared’ in 0.77~3μm,
‘mid infrared’ in 3~6μm, ‘far infrared’ in 6~15μm, and
‘extreme infrared’ in the range of 15μm~1mm.
Spectrum distribution of visible light and infrared is
as below picture.
All objects have their
own temperatures over the absolute zero(-273.15℃, 0K),
and emit electromagnetic waves corresponding to the temperatures.
The higher the temperature is, the shorter the wavelength
becomes and the more the radiant energy emits.For example,
the objects whose temperatures reach to thousands of degrees
like sun or filament of bulb emits visible light, while
the ones near the normal temperature emit infrared. Even
the objects thought to be cold like ice emit infrared.
The hotter an object becomes, the more infrared it emits.
The below image of the space shuttle which is landing
shows that the bottom side is heated during the re-approaching
to the atmosphere. The intensity of infrared measured
corresponds to the temperature of the surface of an object
as you can see in the infrared image of below human face.
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