Thermal imaging cameras, or infrared cameras, are unlike the cameras found in your smartphone. A typical camera observes the wavelengths of light in the visible spectrum that bounce off objects and hit receivers in the camera. The camera will then turn that light into an image. 

Thermal cameras, on the other hand, ignore visible light and seek out something else called infrared. Infrared is a type of low-frequency electromagnetic radiation that is felt as heat, according to the University of Calgary (opens in new tab). This is because infrared radiation excites molecules, causing them to move around and vibrate, causing a temperature rise.

How infrared cameras work

Every object in the known universe gives off some degree of infrared radiation, even if it’s only a tiny bit above the lowest possible temperature, absolute zero (equal to -459.67 degrees Fahrenheit), according to Dr. Christopher S. Baird (opens in new tab), Assistant Professor of Physics at West Texas A&M University. The amount of infrared radiation it gives off correlates to the temperature of an object. 

The hotter an object gets the more infrared it emits. Until an object is hot enough to emit a glow of visible light, such as molten metal, the only way to "see" temperature is with a thermal camera, according to NASA (opens in new tab). 

Thermal imaging cameras use a series of sensors and thermal detectors to estimate the level of infrared in front of them. The onboard sensors convert infrared signals into electrical currents. These currents are then translated into a colour-coded image to show fluctuations in temperature and infrared radiation. 

The infrared camera displays a live infrared map that can instantly outline differing temperatures, according to thermal imaging supplier Teledyne FLIR (opens in new tab).

The concept of thermal imagery is not a recent form of technology, dating back to 1929 when Hungarian Physicist Kalman Tihanyi created the first infrared-sensitive camera. Since then, thermal imaging technology has evolved to become a useful tool in many different industries, including construction and engineering, security, and medical diagnostics, according to thermal imaging supplier Pass (opens in new tab).

Some of the most common uses of infrared cameras include:

Finding wires

Thermal imaging can be used to evaluate different cables and connections that are hidden behind walls. In spotting active wires, engineers can conduct maintenance and detect faults.

Security

Police officers and law enforcement can use thermal imaging to locate criminals in adverse weather, darkness, or in obscured environments such as woodlands.

Health checks

Veterinarians use thermal imaging on the joints of animals to detect hot spots that may be caused by autoimmune conditions, such as arthritis, without the need for surgery.

Finding heat loss

Thermal imaging can be a handy tool for locating cold spots and moisture during building surveys. Also, this can be used to evaluate the overall integrity of the building structure.

Firefighting

Firefighters can use thermal imaging to detect hotspots in a burning building and make decisions on the best course of action. It’s also a useful tool to locate people trapped by smoke.

Discovery of infrared

British Astronomer Sir William Herschel is responsible for the discovery of infrared radiation in 1800. Through a series of experiments, Herschel set a prism at a south-facing window in direct sunlight to direct and separate light into different wavelengths, and subsequently different colours, that make up visible light, according to American Scientist (opens in new tab). 

He then exposed a thermometer to each of the different colours to see how they might change the temperatures on the thermometer. However, what he found was that when the thermometer was placed outside of the visible light, past the red end of the light spectrum, the temperatures continued to increase. What he had discovered was infrared radiation. 

Sir William Herschel conducting experiments that exposed the electromagnetic spectrum.  (Image credit: Getty Images)Additional resources

For more information about infrared light and imagery, check out "A Ray of Light (opens in new tab)" by Walter Wick and "Infrared Thermal Imaging: Fundamentals, Research and Applications, Second Edition (opens in new tab)" by Michael Vollmer and Klaus-Peter Möllmann. 

Bibliography

• Pass, "Thermal Application Guides (opens in new tab)", accessed April 2022. 
• Jack R. White, "Herschel and the Puzzle of Infrared (opens in new tab)", American Scientist, Volume 100, June 2012.
• NASA, "Infrared light (opens in new tab)', March 2004. 
• Jordan Hanania, et al, "Infrared radiation (opens in new tab)", Energy Eduction, University of Calgary, January 2020. 
• Teledyne FLIR, "How Do Thermal Cameras Work? (opens in new tab)", June 2016. 
• Dr. Christopher S. Baird, "Do humans give off radiation? (opens in new tab)", Science Questions with Surprising Answers, July 2013.