In order to understand infrared, it is important to understand something about light. The human eye can detect only a tiny part of the electromagnetic spectrum, called visible light. But there are other forms of light around us such as ultraviolet and infrared. Infrared (IR) light is also a very small part of the entire electromagnetic spectrum and requires a specific device or technology to see it with our eyes.
The 3 Categories of Infrared Light
Infrared light can be split into three categories; near-infrared (near-IR), mid-infrared (mid-IR) and thermal-infrared (thermal-IR). The key difference between thermal-IR and the other two is that thermal-IR is emitted by an object instead of reflected off it. Infrared imaging works two different ways depending on the device or technology used; image enhancement and thermal imaging.
Image enhancement is what most people think of when you talk about night vision. This technology works by collecting tiny amounts of visible light including the lower portion of the infrared light spectrum. This light would be undetectable to our eyes before it is amplified through the night vision device.
How Thermal Imaging Works
Thermal imaging works by capturing the upper portion of the infrared light spectrum which is emitted as heat by objects. Hot objects such as body heat emit more of this light than cooler objects like trees or buildings. Thermal imaging devices capture this heat and transfer it into an image on a monitor. When viewed in a gray scale, hotter things appear white and cooler things appear black. A thermal imaging device transforms thermal energy into visible light with five basic steps:
- A special lens focuses the infrared light emitted by all of the objects in view.
- Infrared detectors are then used to scan this focused radiation. The detectors create what is called a thermogram or temperature map.
- The thermogram is then translated into electric impulses.
- The electric impulses are then sent to a signal-processing unit where they are translated into data. The signal-processing unit is a tiny chip that is embedded on a circuit board which is used to translate the electric impulses into usable data.
- Once translated, the signal-processing unit sends the data to the display where it then becomes visible to the viewer.
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