Thermal imaging is only as good as your ability to interpret it, and that starts with the vocabulary. A handful of technical terms explains why two cameras give different readings on the same target, and why a survey done without the right settings can mislead. This glossary defines the terms that matter most when you are specifying a camera or reading a thermal image with confidence.
Terms that affect measurement accuracy
These are the settings that decide whether a temperature reading is trustworthy. Get them wrong and the camera will still show a number, just not the right one.
Emissivity is a material's efficiency at radiating infrared energy, on a scale from 0 to 1. A matt surface like painted steel has a high emissivity and reads accurately; a shiny surface like bare copper or aluminium has a low emissivity and reads far cooler than it really is unless you correct for it. Setting the right emissivity value is the single most important step for accurate readings.
Reflected apparent temperature is the infrared energy from surrounding sources that reflects off your target and reaches the camera. On low-emissivity surfaces this reflection can dominate the reading, which is why the camera lets you enter a reflected temperature value to compensate.
Terms that describe the camera
These specifications decide what a camera can actually see, and they are where price and performance separate.
Thermal sensitivity (NETD) is the smallest temperature difference a camera can detect, quoted in millikelvin. A lower NETD means the camera resolves finer temperature differences, revealing subtle patterns a less sensitive detector would miss.
Detector resolution is the number of pixels on the infrared sensor, such as 320 by 240. More pixels mean more real temperature measurement points and a sharper image, not just a bigger picture.
Spatial resolution (IFOV) describes the smallest object the camera can measure accurately at a given distance. It ties detector resolution and lens together, and it is why you can see a hot spot but not measure it correctly if it is too small or too far away.
Field of view (FOV) is the area the lens takes in, while the temperature range is the span of temperatures the camera can measure. Both need to match the job, from a wide view of a switchroom to a narrow, high-temperature look at a furnace.
Terms for reading the image
Once the image is captured, these terms describe what you are looking at.
A thermogram is the thermal image itself, a map of surface temperatures rendered in colour. The palette is the colour scheme used to display it, such as ironbow, greyscale or rainbow; changing the palette changes how easily a fault stands out, without changing the underlying data.
Delta T is the temperature difference between a component and a comparable reference, and it is often more meaningful than an absolute temperature. A connection running well above its neighbours has a high delta T, which flags a developing fault regardless of the ambient conditions. IR-Fusion, blending the thermal and visible images, makes it easier to pinpoint exactly which component the hot spot belongs to.
Quick glossary
|
Term |
Meaning |
|
Emissivity |
How efficiently a surface radiates infrared; affects reading accuracy |
|
Reflected apparent temperature |
Reflected energy the camera must be told to compensate for |
|
NETD |
Thermal sensitivity; smallest detectable temperature difference |
|
IFOV |
Spatial resolution; smallest object measurable at a distance |
|
Thermogram |
The thermal image itself |
|
Delta T |
Temperature difference from a reference point |
FAQs
Why does emissivity matter so much?
Because it controls how much infrared a surface radiates. If the camera is set to the wrong emissivity, a shiny low-emissivity surface will read far cooler than its true temperature, which can hide a genuine fault. Setting the correct value, or applying a high-emissivity tape or paint, fixes this.
Is a higher resolution camera always better?
Higher detector resolution helps, but thermal sensitivity (NETD) and correct settings often matter more. A sensitive, well-configured camera in trained hands beats a high-resolution camera used with default settings.
Understanding the terminology turns a colourful picture into reliable data. If you want your team trained to capture and interpret images correctly, or your camera calibrated, explore our thermal imaging surveys and calibration service.