While traditional visible-light cameras capture images of objects radiating light visible to the naked eye, an infrared camera captures infrared light, which the human eye cannot see. All objects radiate some form of heat energy, but some wavelengths within the electromagnetic spectrum are invisible, including infrared. Sensors in an infrared camera capture a particular range of invisible energy emission (700-1000 nm) and then express each heat value (or wavelength) through a set of corresponding colors. The resulting image is called a thermography and is usually viewable on a LCD screen, which displays the thermograph.

Everything with thermal energy emits a certain amount of infrared light. So oftentimes, the terms thermal imaging camera and infrared camera are used interchangeably. Thermal imaging sensors detect infrared radiation and then express each heat value (or wavelength) through a set of corresponding colors that is viewable on a screen.

From a terminology standpoint infrared radiation is defined by having the wavelength in the fixed interval 0.7 - 300 micrometers, this is a convention of the electromagnetic spectrum. However, the term thermal radiation refers to the thermal radiation emitted by all objects - it does not have a wavelength designation. When it comes to infrared cameras however, they are frequently referred to as thermal imaging cameras.

Infrared cameras can be used for many things. They are best for identifying areas of temperature change or difference. An example of this can include finding an animal in the woods or on the water, identifying water leaks in a home or in industrial applications, measuring temperature of people during a pandemic, investigating how well something is insulated, finding components that are overheating on a circuit board, and more.

Water, or other fluid, leaks almost always emit a different wavelength of infrared light compared to their dry surroundings. If you view a puddle of water or a stream of drips it will be identifiable to someone performing an inspection with an infrared camera. Infrared cameras make excellent infrared water leak detectors.

For benchtop applications, usually thermal cameras for printed circuit board (PCB) repair are used to find hot spots on a printed circuit board or other similar electronic device. Hot spots are usually indicative of component failures, electrical shorts, and other circuit board problems. The benchtop thermal imaging camera allows a technician to identify such problems and replace the faulty component without having to dive too deeply into the electrical engineering of the device.

Infrared cameras should not be confused with night vision, which enhances visible light. Because infrared cameras measure light that is not visible to the human eye, they can work in darkness as well as daylight. Some professional photographers enjoy using infrared cameras to capture artistic images because they reflect elements like colors, textures, the sky, trees, and even human subjects differently than visible light photographs. 

One of the biggest advantages of IR is that obstructions like fog, trees or darkness do not hinder the image. That means that police can use IR cameras to find criminals hiding in the bushes, and it also means that home inspectors can use IR cameras to look at hot and cold water pipes inside a wall and watch how the temperature of those pipes change when you turn on the water, even if you can’t see the pipes with your naked eye. IR cameras see things best when there is a contrast in temperature so if there is some sort of temperature contrast inside or behind a thin wall (think drywall, as opposed to brick) then the camera should be able to see it. If the wall is all one temperature and there is no contrast then you won’t see any detail through the wall.

Thermal cameras detect infrared light, which can also be imagined as thermal energy. Water is not transparent to thermal cameras, because water is full of thermal energy - be it cold, hot or in between. So if you bring a thermal camera underwater it will show you the temperature of the water right in front of the camera - not the temperatures of anything in the distance. Similarly, glass usually isn't transparent to thermal cameras - if you point a thermal camera through a window the reading you typically get is the temperature of the glass itself, not the things that you can see through the glass.