Blue background with deer shown in different colored heat signatures through a thermal imager.

What is Thermal Imaging?

Simply put, thermal optics or thermal imaging is a way for us to see things that we can’t normally see with our naked eye. These devices use a special sensor to detect heat signatures and translate them into images we can see.

Thermal scopes, monoculars, and other imagers detect radiation to create an image that allows a hotter object to stand out against a cooler background, marking a clear distinction between objects.

Humans can’t see well in the dark and considering the size of the electromagnetic spectrum, can’t see much at all. For us to be able to see colors, there must be some sort of light source. The electromagnetic spectrum is the word we use to describe the entire range of wavelengths in all light whether it is visible to humans or not. We can’t see most of the electromagnetic spectrum. Our eyes can only see a limited number of colors on this spectrum. This is called the visible spectrum.

Graph showing the light spectrum and which colors humans can see.
We can only see a limited amount of colors on the lightwave spectrum.

So, how are we able to see when there is no light to reflect off objects?

By developing technologies like thermal imaging that allow us to distinguish between objects when there is absolutely no ambient visible light for us to see any color. Thermal imaging is the ability to see heat signatures in any lighting conditions using infrared thermography.

How Does Thermal Imaging Work?

To see things we can’t normally see, we need a device that translates non-visible light into visible light. To do this, we need something that can detect the different temperatures of heat and transfer that data into a readable image.

The light we can see ranges from 380nm to 750nm—which is violet to red, the colors of the rainbow. The infrared (IR) spectrum—which we can’t see—is broken down into near-IR (750nm to 3,000nm,) to mid-wave IR (3,000nm to 8,000nm,) and long-wave IR (8,000nm to 15,000nm.)

The great astronomer and discoverer of the planet Uranus, Sir William Herschel, discovered another spectrum of light (the part we can’t see) called infrared (IR.) While conducting an experiment in measuring the temperatures of colors in the visible spectrum, Herschel put a thermometer in the area directly behind the red. This area measured even hotter than the hottest part of the prism. He called it “dark heat.” We now call it infrared radiation. Infrared, or thermal energy, has a longer wavelength than visible light. You can think of it like radio or ultraviolet rays. We know they are there, we just can’t ever see them.

We can’t see infrared, but we can feel it. It is one way in which living and inanimate objects transfer heat. Everything emits some sort of heat—even ice. Non-living objects, like trees and rocks, absorb heat and emit it. The hotter an object is, the more infrared radiation it produces. That is how thermal imaging allows us to see things that are impossible to see with the naked eye. By detecting the different heat signatures and transferring them to an image on a display, humans can quickly and clearly distinguish between objects. Thermal imagers can detect long-wave infrared—something that night vision and digital night vision can’t.

Black and white thermal image, hogs are shown in bright white contrast to a dark, colder background.
Thermal imaging detects the different heat signatures between objects, so you can quickly identify your target.

Thermal imagers use a microbolometer as the sensor array and a special germanium lens. Germanium is a chemical element that belongs to the carbon group. It is like tin and silicon.

Microbolometers consist of a resistive vanadium oxide or amorphous silicon film that detect electrical resistance changes related to temperature.  These changes in the temperature are converted into a very detailed temperature pattern of electrical signals called a thermogram.  The thermogram is then sent to a signal processing unit that translates the information which is then sent to a micro display that can create the image.  Thermal images are displayed as various shades of white and black or color.  Thermal imagers generally scan at 60hz, 30hz and 9hz and can detect temperatures from -4 degrees Fahrenheit to 3,600 degrees Fahrenheit with a temperature sensitivity of 0.4 degrees Fahrenheit.

There are two types of thermal imagers: un-cooled and cooled.  Uncooled are the most common, are more compact with a built-in power supply, and can operate at normal temperatures. Cooled thermal imagers use a cryogenically-cooled system to keep them below 32 degrees Fahrenheit.  This is necessary to reduce thermally-induced noise to a level below that of the signal from the scene being viewed.  Cooled systems are more expensive, but have a much higher resolution and sensitivity.

Blue background with deer shown in different colored heat signatures through a thermal imager.
You can transition from day to night hunting with a thermal scope without fear of breaking it.

Thermal has several advantages over units that use image intensifier tubes and digital night vision. Since thermal can see at higher wavelengths, it allows you to see through smoke and fog.  Thermal also does not use ambient light to produce images, so users can detect objects in bright daylight or total darkness.  Since thermal is a visual detection of heat, it is easier to detect targets that may be concealed in heavy cover, like bush and vegetation.  A disadvantage to thermal is that it reads heat whether it is produced or reflected by an object, so material such as glass is seen as an opaque surface or a heat reflection.  Pulsar’s thermal imagers can record images directly to an internal memory card or be sent through a video output to a DVR.

Pulsar’s Thermal imaging has plenty of benefits:

  • Unlike night vision, you can use it in daylight
  • You don’t need any light source at all to use
  • Targets that hide under thick and heavy cover are easy to spot
  • You can usually see long distances through weather conditions like fog, smoke and dust

What are the Uses of Thermal Imaging?

  • Firefighters: Use it to detect fire, hot spots, and victims
  • HVAC & Electrical: Can detect loss of heats and leaks from houses and structures
  • Military and Law Enforcement: surveillance, locating targets, search and rescue, recon,
  • Hunting: Locating game
  • Meteorologists: Tracking storms, hurricanes, and other bad weather
  • Medical: Diagnose patients
  • Home security

The development of thermal imaging technology has vastly improved since 1947, when the United States military developed its first thermal imager. Thermal scopes, monoculars, binoculars, and other thermal imaging devices are now available with ultra-high resolutions and refresh rates at prices that are not prohibitive to civilians. They offer more versatility than any other scope you can get on the market. They offer super-fast target acquisition day or night, a clear image in complete darkness, and a vast array of options, like onboard video recording, and different colored reticles.

To shop thermal optics, click here.

Do you have questions about how thermal imaging works or Pulsar’s thermal products? Leave them in the comments section, and our experts will do their best to help.



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