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Thermography or Thermal imaging is the technique of using the infra red spectrum of light to enable viewing and analysing objects in the absence of light in the visible spectrum .Since it operates in the absence of visible light it can be very useful in dark or in harsh weather conditions.
Let us understand more about the nature of light.
The spectrum of light consists of various components as shown
Fig 1.1.light spectrum
Visible range from 400nm to 700nm , ultra violet below 400nm and infrared light above 700nm
Infrared light can be split into three categories:
- Near-infrared (near-IR) – this is closest to visible light; near-IR has wavelengths that range from 700nm to 1300nm.
- Mid-infrared (mid-IR) - Mid-IR has wavelengths ranging from 1300nm to 3000nm. Both near-IR and mid-IR are used by a variety of electronic devices, including remote controls.
- Thermal-infrared (thermal-IR) – this occupies the largest part of the infrared spectrum, and corresponds to the temperature levels. thermal-IR has wavelengths ranging from 3000 microns to over 30000 microns.
The thermal IR part is the one useful in thermography .This part of light unlike others is not reflected by a body but is emitted (or generated) by the body itself .Since different objects emit different amounts of this radiation at different temperatures This fact is used as a characteristic of the object in question and enables it to be identified.