How Can a Thermal Imaging Camera Produce a Picture in the Dark

thermal-imaging-cameraIn 1800, Sir William Herschel conducted an experiment where he discovered that light beyond the red coloured light of the visible light spectrum produces a higher temperature than others within the visible light spectrum. Herschel concluded that there are certain types of light that cannot be seen with our own eyes but, are still present and give off a form of radiation. One such type of radiation is infrared.

What is Infrared Radiation?

Infrared is invisible, electromagnetic radiation. As part of the electromagnetic spectrum, infrared has longer wavelengths than those belonging to visible light, but fewer wavelengths than microwaves or radio waves. There are many other types of radiation such as microwaves, Gama rays, ultraviolet rays etc. that are also beyond the visible light spectrum and are unable to be detected by the human eye.

Microns and Micrometres (μm)

Not only used to measure cells and bacterium, the micrometre is also a common unit of measurement for wavelengths of infrared radiation. Light with wavelengths from 0.7 micron to about 0.1 millimeter in diameter is infrared light. The band of infrared light is a thousand times wider than that of visible light.

What is the Difference Between a Thermal Imaging Camera, a Digital Camera and Night Vision?

Because most of the thermal radiation emitted by objects close to room temperature is infrared, a thermal imaging camera will be able to produce a picture in the dark as it’s sensors will pick up the various temperatures of the area in focus. This will render an image full of “false colours”, which are the reds, greens, yellows, blues and purples that are most prominent in a thermal image. By contrast, a digital camera will render an image full of “true colours”, as they are displayed in nature. Night vision only works with small bits of natural, visible light. When a small source of visible light is sensed, night vision technology will amplify the light source rendering more objects visibly displayed.


In order to understand further how a thermal imaging camera can produce a picture in the dark, we must look at how many of the camera’s core components work. The core of the thermal imaging camera is the microbolometer. The microbolometer is made up of an array of pixels or sensors called the focal plane array. These pixels pick up the infrared radiation and then render it through a germanium lens so we can visibly see the image as it appears on a screen.

Germanium Lens

This expensive metal is a great transmitter of infrared radiation and is used instead of a glass lens found in a digital camera. Germanium is transparent in the infrared wavelengths, this makes it a crucial infrared optical material that is easily cut and polished into lenses, screens and windows. When germanium is used as the front optic in a thermal imaging camera, it works in the 8-14 micron range.

Infrared Thermography

Infrared thermography is the rendering of temperatures given off by infrared radiation. Most thermal imaging cameras are able to show not just an image of the infrared radiation it senses, but also the various temperatures of the objects in view. Because a thermal imaging camera produces an image based on temperatures, a light source need not be present.


To conclude, we have seen all of the elements of a thermal imaging camera, how the components work, we have defined infrared radiation, its forms of measurement and the usefulness of a thermal imaging camera and how it can render an image based on temperatures. But does all of this explain how a thermal imaging camera can produce a picture in the dark? Yes, it does! This is because we’ve gone over the key fact that a thermal imaging camera senses infrared radiation, a heat source, so it does not require any visible sources of light on the electromagnetic spectrum. Not only can infrared technology sense temperatures, but infrared telescopes can produce the most detailed and furthest images seen in the universe, which essentially means that with the right kind of lens, infrared radiation can allow us to render images of stars that might have already died in the unlikely event that we were able to travel there to see it with our naked eyes. Infrared radiation not only allows us to see objects in the dark, but it can allow us to see objects in the past.

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