Thermal Imaging Cameras: How Do They Work? 

 March 27, 2021

By  Randy Angwin

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Last updated on July 11, 2021

Everything around us radiates heat. In the electromagnetic spectrum, there are wavelengths called visible light that human eyes can view. Traditional cameras can detect and capture visible light, but visible light only forms a small portion of the spectrum.

The naked eye cannot see other types of wavelengths such as infrared radiation. To capture and analyze these types of wavelengths, devices such as thermal imaging cameras can be used.

What is Infrared Radiation?

Infrared Radiation

Discovered by the astronomer Sir William Herschel in the 1800s, infrared radiation is a type of radiant energy that the human eye cannot see, but the skin can feel as a warm sensation. It has a longer wavelength than visible light, but has a shorter wavelength compared to radio waves. It interacts with molecules and causes them to move faster, which increases the internal temperature of objects. It also appears in different colors that represent increasing temperatures.

The concept of thermography goes way back to the 1800s, but it gained popularity in the 1920s when it was used in British anti-aircraft defense after World War I. Hungarian physicist Kálmán Tihanyi invented the first infrared-sensitive night vision television camera, which he called the Evaporograph. This thermal imaging camera was used in detecting enemy aircraft.

Today, infrared radiation is used in many applications, including cooking, meteorology, astronomy, night vision, military defense, and thermal imaging. Electronic devices such as remote controls, game consoles, CCTV cameras, and biometric scanners, also use infrared light.

What are Thermal Imaging Cameras?

thermal imaging camera scan

Thermal imaging cameras, also called thermal or thermographic cameras, can detect heat or thermal energy and translate it into visible light. Specifically, thermal imaging cameras capture infrared radiation which is otherwise invisible in the electromagnetic spectrum.

Thermal cameras are available in different forms. Some are handheld and can be operated using a trigger to capture images. Others come in larger versions that are wheeled and held by two hands.

How Do Thermal Cameras Work?

A thermal imaging camera comes with sensors that can detect temperature differences. When the lens of one is pointed at a particular object, it detects and scans the object's infrared energy and captures temperature information from different points in the sensor's field of view.

The detector elements of the thermal camera then use this infrared energy to create a detailed temperature pattern, also known as the thermogram. The thermogram is converted into electronic signals which are sent to the circuit board.

The signal processing unit transmits the electronic signals to the thermal camera's display screen, which can be seen as images in different color palettes. The variation in colors typically depends on the differences in the intensity of infrared emissions captured by the device's detector.

What is Thermal Imaging?

Infrared spectrum

Thermal imaging refers to the process of converting thermal energy into visible light, making it possible to analyze any object or its surrounding area. It is especially useful at night or in places where no light is available. As objects and living things emit heat energy, thermal imaging devices can easily detect them even in total darkness.

The amount of thermal energy or radiation that an object emits is the heat signature. The hotter the object is, the more radiant energy it transmits. A thermal imaging device detects the surface temperature of an object to generate an image. This technology can also distinguish differences in heat levels. 

What Do Thermal Imaging Colors Mean?

thermal image

Since infrared radiation is invisible, one way to analyze thermographs or thermal images is through color mapping. As mentioned before, thermal cameras have a sensor array that captures the heat emitted by an object. Along with these sensor arrays are pixels that show the full temperature of the object in the thermal image.

In the light spectrum, the color map or palette differentiates the heat levels of objects. Warm surface temperatures are in the red or yellow range, while cooler surface temperatures are in the blue or purple portion of the spectrum.

Can Thermal Cameras Work at Daytime or Where There is Light?

Thermal cameras are useful at night, but they also work fine during daylight. Thermal imaging cameras detect heat instead of light, so they can be useful in seeing objects or animals that camouflage in certain environments. Thermal cameras can also detect living or non-living things in foggy conditions.

What Can Thermal Cameras Detect?

Thermal cameras are an integral part of different industrial and commercial applications. They are also useful in homes. Below are some uses of the thermal cameras:


Thermal images allow firefighters to spot sources of fire. They also enable rescuers to see people through smoke-filled, low-visibility rooms.

Law Enforcement

Thermal imaging cameras can identify thieves hiding in dark areas, preventing potential ambushes or escapes. Police cars and helicopters also use IR technology as support to track down someone who is trying to flee from a crime scene.


Infrared devices can see other vessels at sea, even without any supporting light source. They can also help in searching for and rescuing people whose boats have capsized and are stuck in dark waters.

Road Safety

Infrared cameras make driving safer and help prevent road accidents, especially on dark roads.

Building Safety

An infrared camera can detect gas leaks in industrial sites. They can also be used in conducting periodic safety checks of electrical equipment.


Thermal imagery is used for military hardware such as drones and other surveillance equipment. They help mitigate risks when driving or flying in low-light conditions, preventing collisions and accidents.


Ecologists use thermal images to conduct wildlife research. They are also useful in animal surveillance and rescue support efforts.

Pest control

Thermal imaging can detect pests hiding in residential, commercial, or industrial buildings, without technicians having to physically go through roofs, ceilings, or attics.

HealthcareThermal imaging devices are non-invasive tools that can help detect various disorders in the body.


Infrared cameras are handy when camping to view wildlife, even at night. There are also phone apps that allow users to take thermal camera photos.

About the author 

Randy Angwin

Randy Angwin holds a master of science degree from University of Florida. He is an expert in infrared and night vision technology. His knowledge helps us staying on top of the latest trends in the thermal industry. When not working, Randy likes to hunt and spend time with his two German shepherds.

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