What Does Thermal Imaging Do?

All objects emit infrared energy as heat. By detecting the very subtle temperature differences of everything in view, infrared (or thermal imaging) technology is able to reveal what would otherwise be invisible to the naked eye. Even in challenging weather conditions or complete darkness, thermal imaging gives the user the ability to see the unseen.

Thermal imaging technology was first developed for military use and has since been adopted by law enforcement, fire and rescue teams, and security professionals, and is now being used in more commercial applications, such as hunting, game keeping, boating, and leisure.

What to Look For in a Thermal Imager

When considering purchasing a thermal imager, there are a few essential factors that need to be taken into consideration to ensure you find a product which is best suited to your needs. See below to discover the key features that make up a thermal imaging device.

A Simplified Explanation of How Thermal Imaging Works

  • The objects in view all emit infrared energy (heat), which is invisible to the naked human eye.
  • A thermal imager’s germanium objective lens focuses the heat onto the device’s microbolometer (thermal sensor).
  • The signal processor then converts the information into a visible format, presented on the device’s eyepiece.

Thermal Sensor Size

Similar to digital cameras, thermal sensors are measured in pixels; generally speaking, the bigger the sensor the better the picture, as a larger sensor can capture more detail — so you should prioritise finding the highest resolution you can within your budget. As an example, Pulsar thermal imagers use one of four different sized sensors with its own designation: XM models use a 320×240 thermal sensor; XQ models use a 384×288 thermal sensor; XP and XG models use a 640×480 thermal sensor; and XL models use a 1024×768 HD thermal sensor.

Most specification sheets will state the detection (you can detect ‘something’ is present), recognition (you can recognise it is human) and identification (you can identify its a man/woman, model of car etc) ranges of a man-sized target with a emphasis on the detection range.

Thermal Sensor Pixel Pitch

A thermal imager’s pixel pitch (µm) refers to the distance between the centre of the pixels. A smaller pixel pitch results in finer image quality and a physically smaller thermal sensor, whereas a larger pixel offers more sensitivity but results in a physically larger sensor. A sensor with a smaller pixel pitch will have a greater base magnification than a thermal imager with the same size lens and a greater pixel pitch.


The Noise Equivalent Temperature Difference (NETD) is a measurement of the smallest temperature difference a thermal imaging device can detect. The lower this NETD value, the more sensitive the device becomes — performing better than a device with a larger NETD value in conditions that are challenging to thermal imagers (such as cold, fog, and rain). A device’s NETD rating is an important indicator as to how well it will perform.

Refresh Rate

A high refresh rate (such as 50Hz) is best when choosing a thermal imager. A high refresh rate will result in a smooth image when panning or tracking fast-moving objects. Also known as frames per second (FPS) or frame frequency, the frame rate determines the rate at which the device produces consecutive images and therefore the refresh rate and smoothness of the moving image you can see. Most models’ specifications will display this rate in Hz ranging from 9 to 50. A higher frame rate means a smoother image when panning or tracking a moving target.

Optical Magnification

When considering which thermal imager is best for your needs, you’ll need to determine the environment in which it will be used. The magnification will partly determine the ranges, but it’s also worth remembering that increasing the magnification reduces the field of view. Take this into consideration when determining whether the unit will be used more for long-range observation or if its primary use will be in confined space.

Detection Range

The detection range (and, consequently, the recognition and identification ranges) varies from model to model. To find the best match for your requirements it is essential you determine exactly what you will be using the device for to ensure it is able to perform under the conditions. A thermal imager’s detection range is determined by a combination of optical magnification and sensor resolution.

Take a look at our quick video guide to see the essential factors you should consider before buying a thermal imaging device:


Taking Thermal Imaging Devices Out the Country:

All thermal imaging devices with a frame rate above 9Hz (or weapon mounted, regardless of frame rate) are strictly controlled by ITAR regulations and are subject to UK Government Export Licencing Regulations. If you wish to take your device abroad with you, a licence will need to be obtained prior to the export from the UK, even if this is only for a temporary export (e.g. holiday). Some countries may be embargoed — in these cases no thermal imagers or night vision devices can be taken or exported to them. It is the responsibility of the exporter, whether it be a company or an individual, to ensure that such a licence is obtained. Failure to comply is a criminal offence. Find out more here.

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