How Does a Thermal Camera Work?

Indeed, a thermal camera (a.k.a., infrared camera) sees far beyond what our human eyes can see. By doing so, it can give us unmistakable signs of the birth of a star hundreds of thousands of miles away. Had we relied on just visible light (e.g., smartphone camera), we would miserably fall short. And fumble.

In fact, Hubble Space Telescope, as powerful as it is, won’t be able to detect such a groundbreaking moment. NASA’s low-orbit space telescope might be able to give you a spectacular image of a beautiful nebula far, far away. And yet, it won’t give us a hint on the rise of a fledgling star about to be born inside that nebula. No, sir. The images covered with intergalactic dust would obscure the monumental event. But not if an infrared camera can’t help it. 

Closer to home, thermal cameras have been making waves globally in the fight against COVID-19, the dreaded virus that has kept our movements drastically measured. Without a doubt, these cameras have taken center stage. It might not directly detect the presence of the pathogen. But, truth be told, no device can detect fever, a top symptom of viral infection, from a safe distance better than the infrared camera. Small wonder why it has become a permanent fixture in the entrances of malls and other public places these days. 

Therefore, it’s but paramount that you take a closer look at how thermal cameras work. By acquiring greater knowledge, you’d be able to maximize the use of the thermal camera as much as it has upended our lives on the planet. And to a large degree, gain greater productivity and efficiency when you want to make things work. 

Principle First

Right off the bat, you might be bewildered at how an infrared camera can detect the birth of a star. But that’s just the tip of the iceberg. Infrared astronomy can discover a lot more about our known universe because it goes beyond visible light. Or what a pair of human eyes can see. 

So first things first, know that infrared light is invisible. Unlike the normal things that we see every day, we cannot use human vision to see infrared light.

It’s no accident that Sir William Herschel, the British astronomer who discovered infrared radiation (IR) in 1800, didn’t even know that infrared radiation was there. At least not until he saw its effects. Using the prism experiment made familiar by Sir Isaac Newton, William using thermometers to measure the temperature of each color produced by the sun’s light. He realized that the heat increased as the colors turn to red. Finally, he bumped into the “invisible light” which is hotter than red. And that’s how infrared, or heat energy was discovered. 

Take note that infrared energy and visible light are part and parcel of the electromagnetic spectrum (ES), the various frequencies of electromagnetic radiation. In graphics form: 

Electromagnetic Spectrum

Figure A. Infrared, Visible Light and the Electromagnetic Spectrum

So, you must realize that it would be futile to compare regular cameras and thermal cameras. Regular cameras, the ones you have on your smartphone, use visible light energy to capture pictures around you. The same holds true for the human eyes which also make the most of visible light energy to see. 

Thermal cameras detect the presence of heat (and not visible light). And from that input form a visual representation via digital or analog outputs. Therefore, it sees only heat energy and not the picture our eyes are accustomed to. 

Take note that everything on the planet emits heat energy even a block of cold ice. The hotter an object gets, the more thermal energy it emits. It’s incumbent then that a thermal camera detects an object’s specific thermal profile, also dubbed as its heat signature. Objects placed side by side can have different heat signatures. However, extreme heat such as fire can affect the heat signature of objects that get close to it. 

Indeed, it’s the job of the thermal camera to portray how much thermal energy an object emits. While a regular camera can give you a visual representation of the objects around you in stunning colors, it cannot depict the heat energy of said objects. On the other hand, a thermal camera can show you various heat energy of the objects around you, but it can’t give you a vivid picture of your surroundings. 

Infrared astronomy can detect the birth of a new star better than any powerful telescope because it can keep track of energy emissions from outer space. When new stars are born, they emit a certain unmistakable infrared light betraying their presence. While the usual celestial telescopes won’t be able to see through all the galactic clouds of dust and nebulae, powerful infrared telescopes detect the sudden bursts of this intergalactic energy.

Inside the Thermal Camera: How It Works

Knowing what infrared radiation is one thing and capturing it is another. We must understand that the thermal imaging camera that we know of today is a product of a long-and-winding process that took decades to perfect. For one, our infrared cameras today are powerful yet user-friendly. So unlike those used by firefighting decades ago which were not only hefty in weight but also detrimental in price. 

First things first. Let’s give credit where credit is due. Though it was Sir William Herschel who made the world aware of infrared radiation, it was a Hungarian physicist and inventor Kálmán Tihanyi who invented the first infrared-sensitive camera in 1929. In this regard, we can refer to Tihanyi as the “man who made us see the invisible.”

As an infrared camera is geared towards capturing heat energy in its surroundings, its main components are designed to process infrared radiation. That’s especially true of the input unit. We’re talking about the lens and the sensors, the path through which infrared radiation must pass through. 

Inside the thermal camera

Figure 2. Inside the thermal camera

  1. Lens

Right off the bat, think of the lens of the thermal camera as you would your eyelids. If your eyelids don’t open, you won’t be able to see your surroundings. Not a single thing. For its part, the thermal camera must have a lens that allows IR and its various frequencies to pass through. Only then can a signal be processed by a sensor. 

And this is where an IR camera and a standard camera (the one on your phone) diverge paths. Unlike regular cameras, the IR camera’s lens must not be made of glass. Take note that glass blocks long-wave infrared radiation (LWIR), frequencies most useful for thermography. 

Thus, lenses are usually made of Germanium, Zinc Selenide, Calcium Fluoride, or Sapphire. By doing so, the lens can cater to the electromagnetic spectral range of thermal radiation from 7 to 14 μm. As most of these materials have a high refractive index, it’s paramount that anti-reflective coatings be applied to the lenses to correct deflections. 

  1. Sensor

The heart of the thermal camera is the sensor. This is where infrared radiation passes through a thermal detector. Such a detector directly responds to the thermal increase that happens as a consequence of the absorption of incoming infrared light. 

However, over time there are two most prominent ways to get this done. The more recent and common technology used today is via a microbolometer while the other way is to use pyroelectric materials. Details below.


By principle, a microbolometer is a device that’s sensitive to radiation. The first bolometer was invented by Samuel Pierpont Langley (1834 - 1906), an American physicist/astronomer inventor. 

Any radiation that directly hits a microbolometer’s absorptive element causes a corresponding rise in temperature. The greater the absorbed energy is, the higher the temperature becomes. Such temperature change can be directly measured using a resistive thermometer. And read out as an electronic signal to produce an electronic image. In essence, a microbolometer is composed of a thin layer of metal which is then connected directly to a thermal reservoir (of constant temperature) via a thermal link. 

The sensor array is home to thousands of detector pixels that are arranged in a grid. Know that each pixel in the array reacts to the infrared radiation that directly hits it producing a resistance that can then be translated into an electronic signal. The signal from each pixel is processed by applying a mathematical formula that forms the basis of the color map of the captured temperature of the object. The ensuing picture of colors is then sent to the camera’s processing unit for display. 

Know that each of the pixels has one microbolometer for greater accuracy. Due to this, thermal cameras have a rather low resolution compared to a smart TV or a regular camera. The fact is usually, 640x480 is considered high resolution already for a thermal camera. 

The microbolometer-based thermal camera is also called uncooled thermal cameras as there’s no need to have a separate cooling mechanism to operate the microbolometer sensors. The immediate advantage is these IR cameras are way lighter compared to traditional cooled models. 

Pyroelectric Materials 

These are thermal imaging cameras that use a cooled sensor detector. A glorious example is lithium tantalate. The material generates a minute electric voltage in direct response to changes in the temperature. In this sense, it detects the infrared photons directly. It is photovoltaic as opposed to uncooled microbolometer-based thermal cameras that are using photoconductivity. 

Though they offer a host of advantages such as long-distance infrared detection and more refined temperature difference results, cooled thermal cameras are gradually losing ground to uncooled devices. That’s primarily because of their more expensive price tag and their bulky nature. As its imaging sensor has to be integrated with a cryocooler, these infrared detectors are heavy by today’s standards. Worse, the moving parts in the cryocoolers easily wear out over time. 

  1. Image Processor

Once the infrared radiation is acquired, data must be processed to create the output as seen on the IR camera screen. Data processing involves pre-processing, feature extraction, and classification. Take note that filtering is used to eliminate noise or unwanted data. Here, an algorithm or mathematical equation is used to come up with a viewable image. 

  1. Display

This is where the data from the camera processor is transformed into an electronic signal. Remember that said data is taken from each pixel (non-cooled). By applying the mathematical algorithm, a color map can be produced. This represents the apparent heat signature of the objects being investigated. Before, non-colored or black-and-white representations were common in thermal imaging displays. 

Top Unique Thermal Camera Applications

Scanning the Universe

Visible light can fall short when it comes to the expanse of the universe. In fact, there are bajillion objects in the universe that are way too cool in temperature and distinctively faint making them impossible to locate via visible light. And yet, an IR camera will have no issue detecting these. As heavenly bodies (as large as they are) emit infrared waves, locating and monitoring them would be a lot easier. 

A classic example is Saturn’s aurora. NASA was able to monitor the movement of the planet’s lights and consequently compare it to those of the Earth (Aurora Borealis). 

Even better, armed with a longer wavelength than visible light, infrared waves can go through nebulae and immense dusty regions in outer space with better results, less scattering, and greater integrity. Thus, we can look deeper into the origins of our known universe and discover the birth of stars and other galaxies. 

Auto Repair

Imagine how far easier it will be for you and the mechanic to locate your car’s problem. You won’t have to second-guess if it’s the fuse box or the car’s electrical system. By using a handy infrared camera you can pinpoint the source of the problem. Take note that overheating is a telltale sign of automobile trouble. 

And just like when a home inspector uses one to detect energy loopholes in your living space, a thermal camera can be used to deal with car issues. Saving precious time and energy in the process. 

Animal Health

We have witnessed how a thermal camera can be instrumental in thwarting the advance of the COVID-19 menace. Plus, the technology should prove to be crucial in reopening facilities in post-pandemic times. State-of-the-art product offerings epitomized by PerfectPrime’s IR280H, the world’s first handheld thermal camera with never-before-heard 0.3°C (0.6°F) level of accuracy, should be instrumental in creating a safer world, free from the clutches of the virus. Not only do you get faster fever detection but you also get a prime offering without blowing a huge hole in your wallet.

But thermography also benefits pets. As our fave animals - from dogs, cats to horses - cannot verbalize their pain, being able to determine if they are suffering from health issues is spot on. Even if you know they’re suffering, locating the heart of the problem is another challenge altogether. 

And this is where once again, a thermal camera comes to the rescue. The presence of heat has always been a good indication of health issues in animals. This is especially true when it comes to fever, infections, and possible inflammations. Fever detection in humans brings that to light. Small wonder why infrared cameras have become a standard feature in many establishment entrances all over America. 

By deploying infrared technology, you can detect possible hot spots areas in your pets. It doesn’t matter if your pets are living with you in a household, or in a farm. You and your veterinarian can zero in on a problem area in no time. 

Indeed, you save energy and time, not to mention your precious finances. Best of all, you save lives. And that’s the beauty of a thermal camera in your hand. 

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