Everything You Need To Know About Thermal Imaging Cameras

11 Aug.,2022


infrared lenses

valuable companion to emergency response units, medics, product manufacturers, engineers and maintenance workers across a wide variety of industries - as well as an increasingly affordable option for many different types of hobbyists and enthusiasts at home.

Quality thermal imaging cameras are often sold in the UK in a selection of user-friendly ergonomic designs and offer temperature detection capabilities spanning a broad range of heat sensitivities. This makes them a

On a colour thermographic display, warmer components or regions will show up as reds, oranges and yellows, while cooler parts will typically be shown as purples and blues (green usually indicates areas that are roughly at room temperature). Because they measure infrared radiation, and not visible light, thermal cameras are also useful for identifying heat sources in very dark or otherwise obscured environments.

This is often rendered as a colour map in modern IR cameras, although black-and-white displays are still preferred for certain applications due to their reduced visual ‘busyness’ and improved capture of fine detail.

Visible light forms only a small part of the electromagnetic spectrum, and the only part we can actually see. When pointed at an object or area, the sensor on a thermal detection camera allows the user to view the otherwise invisible infrared spectrum, which exists at wavelengths between visible light and microwaves.

The key component of a thermal camera is a heat sensor attached to a special type of lens, which is then adapted to work alongside standard image-capture technologies. This allows engineers to quickly identify regions of excessive temperature or sources of wasted heat energy, such as overheating components or potential thermal insulation gaps in building inspection.

Although thermal imaging camcorders were still a long way off, Herschel’s findings were quickly used to produce a number of early thermocouple -type modules, which could detect the unseen heat emanating from warm bodies at a considerable distance. His initial discovery was further developed by many other physicists, engineers and inventors in subsequent years:

However, viewing heat energy as an infrared spectrum display isn’t actually a new concept by any means; in fact, the roots of the basic thermography principle were established more than 200 years ago by the German-British astronomer William Herschel:

It’s only in the past few years that the mass production of thermal imaging technologies has reached a point where handheld thermographic cameras (also known as heat cameras, thermal detection or infrared cameras) are now an accessible option for most civil applications and/or hobbyist use.

Today, the plummeting cost of cutting-edge technologies like smart sensors, microcircuitry and WiFi connectivity make thermal video cameras a popular addition to many professional and household engineering, repair, design, creative and hobbyist toolkits.

Many types of thermal imaging camera will also include a standard shooting mode that works with the visible light spectrum, much like any other point-and-click digital camera. This allows for easy comparison of two identical shots - one in IR and one in normal mode - to help quickly identify specific problem areas once the user steps out from behind the lens.

The sensor array is constructed as a grid of pixels, each of which reacts to the infrared wavelengths hitting it by converting them into an electronic signal. Those signals are then sent to a processor within the main body of the camera, which converts them using algorithms into a colour map of different temperature values. It’s this map which is sent on to be rendered by the display screen.

In order to do so, the camera must first be fitted with a lens that allows IR frequencies to pass through, focusing them on to a special sensor array which can, in turn, detect and read them.

An infrared, IR or thermal imaging camera works by detecting and measuring the infrared radiation emanating from objects - in other words, their heat signature.

Thermal imaging camera usage questions

Alongside frequently asked questions about how thermal imaging cameras work in general, there are also a number of common queries regarding specific use scenarios and the effectiveness of the technology in particular environments or applications.

In this section, we’ll examine a few of the better answers and the reasoning behind them.

Why do thermal imaging cameras work better at night?

Thermal imaging cameras tend to work better at night, but it has nothing to do with the state of the surrounding environment being light or dark.

Rather, because the ambient temperature - and, more importantly, the core temperature of otherwise-unheated objects and environments - is nearly always significantly lower at night than during sunlight hours, thermal imaging sensors are able to display warm areas at higher contrast.

Even on relatively cool days, heat energy from the sun will be gradually absorbed by buildings, roads, vegetation, construction materials and more while ever it’s daylight outside. And, for every degree these sorts of objects gain in ambient temperature over the course of the day, they become less clearly distinguishable from other warm objects the camera’s sensor is being used to detect and highlight.

For the same reason, most thermal imaging cameras will display warm objects in sharper contrast after several hours of darkness, rather than just after the sun sets - and, even during full daylight hours, they’ll usually be more effective in the early morning than in the middle of the afternoon.

Do thermal cameras work through glass?

You may be surprised to learn that thermal imaging cameras don’t generally work through glass.

A full explanation of the technical reasons for this would be somewhat complex from a physics standpoint, but the principle is pretty straightforward. In essence, a sheet of glass allows visible light through but acts a bit like a mirror for infrared wavelengths (this is why the lenses on IR cameras are commonly made from germanium or zinc selenide, not glass).

If you were to point a thermal detection camera at a window, what you’d see onscreen wouldn’t be a clear thermal rendering of what’s on the other side, but most likely a blurry mess - and possibly a vague reflection of yourself holding the camera!

It’s not an absolutely hard and fast rule; certain infrared frequencies can pass through glass, and certain types and configurations of glass may allow varying degrees of infrared to pass through. Car windscreens tend to yield better results than standard household glazing, for example.

In most cases though, the image will be largely obscured by infrared reflection from the ‘wrong’ side of the glass, overlaid in varying degrees of opacity. At the very least, the object being viewed will lack significant detail and contrast.

In short, you won’t want to be using a thermal imaging camera to get accurate readings through glass (or various other types of highly reflective surfaces).

Do thermal cameras work underwater?

Thermal cameras don’t tend to work well underwater. The reasons are, in part, related to the issues with glass outlined above.

Water blocks a lot of infrared wavelengths, much as an opaque barrier blocks visible light wavelengths. In the same way that we can’t see through paint, infrared sensors can’t ‘see’ through any significant depth of water, because the waves it detects don’t pass through water easily.

Water also provides another challenging issue for IR cameras, related to thermal conductivity and specific heat. Water has a much higher heat capacity than air, requiring four times as much energy to raise or lower the temperature of an equivalent volume by one degree.

In practical terms, this means that objects lose (or gain) their own heat energy relative to water much faster, and over shorter distances. For thermal imaging purposes, objects are therefore naturally harder to differentiate when submerged than they would be in the air.

Can thermal imaging cameras see through walls?

Well, no - but to be fair, they don’t ‘see through’ anything at all. A thermal imaging camera detects the surface temperature of the first object in its line of sight; point one at a wall or other solid surface, and it will register the heat being radiated outward by that surface.

Because most buildings are engineered and insulated to trap heat, exterior thermographic imaging seldom reveals much about what’s going on inside and vice versa. There are some caveats here: an IR camera can be used to detect extreme heat radiating from behind a wall (such as in the case of a house fire), because the wall itself would quickly heat up too.

Similarly, some thermal cameras are sensitive enough (up to +/- 0.01 Celsius) to register the warmth given off by a person, for instance, standing against the opposite side of a sufficiently thin (and cold!) wall - but only if they remain in place long enough for their own body heat to partially transfer through the materials of the wall in that spot.