Thermal imaging works by detecting the infrared radiation that every object emits and converting it into a visible image that maps surface temperature differences. The technology is entirely non-contact, works in total darkness, and reveals faults invisible to the naked eye. This article explains the underlying physics, the components inside a thermal camera, emissivity, practical applications in electrical and building maintenance, and what training you need to use the technology effectively.
What is thermal imaging?
Thermal imaging, also called infrared thermography, is the process of capturing the heat energy radiating from an object's surface and displaying it as a colour-coded image called a thermogram. Every object with a temperature above absolute zero (−273.15 °C) emits infrared radiation. The hotter the object, the more radiation it produces. This relationship is described by the Stefan-Boltzmann law, one of the foundational principles of thermal physics.
The discovery of infrared radiation itself dates back to 1800, when Sir William Herschel used a prism to split sunlight and placed a thermometer just beyond the red end of the visible spectrum. He measured a temperature rise, proving the existence of an invisible form of radiation. More than two centuries later, that principle drives a technology used daily across electrical maintenance, building diagnostics, industrial process monitoring, and emergency services.
What makes thermal imaging so valuable is its non-contact, non-invasive nature. You do not need to touch, de-energise, or dismantle anything to get a reading. That single characteristic is what makes it indispensable for inspecting live electrical equipment.
How a thermal imaging camera works
A thermal camera captures infrared energy through a specialised lens, focuses it onto a detector array, and processes the signal into a visual image. The core components are quite different from those in a standard digital camera.
|
Component |
Function |
Typical specification |
|
Infrared lens |
Focuses IR radiation onto the detector; made from germanium or chalcogenide glass because standard optical glass blocks IR |
Germanium, anti-reflective coated |
|
Detector (sensor) |
Converts IR energy into an electrical signal; most professional cameras use an uncooled microbolometer array |
Resolution from 160 × 120 up to 640 × 480 pixels or higher |
|
Signal processor |
Assigns a temperature value to each pixel and maps it to a colour palette |
Accuracy typically ±2 °C or ±2% of reading |
|
Display |
Shows the thermogram in real time |
LCD touchscreen, often with visible-light camera overlay |
|
Software/storage |
Records radiometric images for later analysis and reporting |
Radiometric JPEG; report software such as FLIR Reporter |
The microbolometer is the most common detector type in portable professional cameras. It is "uncooled", meaning it operates at ambient temperature without cryogenic cooling. Each tiny element in the array absorbs incoming IR radiation, heats up fractionally, and changes its electrical resistance. The processor reads those resistance changes thousands of times per second to build a live thermal image.
Colour palettes (ironbow, rainbow, greyscale, and others) are simply visual conventions. They do not change the underlying data; they just make temperature differences easier for your eye to pick out. Most thermographers use the ironbow palette for general work because it provides good contrast across a wide temperature range.
Infrared wavelengths and the electromagnetic spectrum
Infrared radiation sits between visible light and microwave radiation on the electromagnetic spectrum, spanning wavelengths from roughly 0.7 µm to 1,000 µm. Thermal cameras for electrical and building work typically operate in the long-wave infrared (LWIR) band, between 8 and 14 µm. Why that specific window? Because the Earth's atmosphere is relatively transparent to IR in that range, and most objects at everyday temperatures (from about −20 °C to several hundred degrees) emit strongly in it.
Some specialist cameras use the mid-wave infrared (MWIR) band, roughly 3 to 5 µm. These tend to be cooled detectors used in research, military, and high-temperature process applications. For the vast majority of electrical and building thermography, LWIR uncooled cameras are the standard.
Emissivity and why it matters
Emissivity is the measure of how efficiently a surface emits infrared radiation compared to a perfect theoretical emitter (a "blackbody", with an emissivity of 1.0). If your camera assumes an emissivity of 0.95 but you are pointing it at polished aluminium (emissivity around 0.05), the temperature reading will be wildly wrong. Getting emissivity right is one of the first things you learn in any serious thermal imaging training course.
|
Material |
Typical emissivity |
Notes |
|
Black electrical tape |
~0.95 |
Often used as a reference target on low-emissivity surfaces |
|
Painted steel (any colour) |
0.90-0.95 |
Paint colour has minimal effect; it is the surface finish that counts |
|
Oxidised copper busbar |
0.60-0.80 |
Varies with degree of oxidation |
|
Polished aluminium |
0.03-0.10 |
Highly reflective; readings unreliable without correction |
|
Concrete / brick |
0.90-0.95 |
Good target for building surveys |
Practical workarounds for low-emissivity surfaces include applying a strip of high-emissivity tape, adjusting the emissivity setting on the camera, and accounting for reflected apparent temperature. Shiny, polished metals remain the biggest accuracy challenge in electrical thermography.
Thermal imaging vs visible light photography
A standard camera captures reflected visible light. A thermal camera captures emitted infrared radiation. That is the fundamental difference, and it explains why thermal cameras work in complete darkness, through light smoke, and in fog. They are not dependent on any external light source.
However, thermal cameras cannot see through solid walls, glass, or metal enclosures. They image surface temperatures only. A hot cable behind a plasterboard wall may warm the wall surface enough to create a detectable pattern, but the camera is reading the plasterboard, not the cable itself. This is a common misconception worth correcting early.
Modern professional cameras often include a built-in visible-light camera that overlays the thermal image onto a standard photograph, a feature variously called IR-Fusion, picture-in-picture, or MSX. The Fluke Ti401 PRO, for example, offers this capability. The overlay makes it far easier to identify exactly which component the hot spot corresponds to, especially in a crowded distribution board. You can read more about the advantages of IR-Fusion technology for practical inspection work.
Applications in electrical maintenance and predictive maintenance
Electrical thermography is one of the most established predictive maintenance techniques. A thermal camera survey of live switchgear, distribution boards, busbars, motors, and cable terminations can reveal:
- Loose or corroded connections (showing as localised hot spots)
- Overloaded circuits or phases (one phase running significantly hotter)
- Deteriorating insulation or partial discharge activity
- Failing bearings in motors and drives
- Unbalanced loads across a three-phase supply
Because the inspection is entirely non-contact and non-invasive, it can be carried out on energised equipment without interrupting operations. This is the real advantage over periodic shutdown inspections; you survey the equipment under load, which is the only condition where thermal faults actually present themselves.
How often should you survey? There is no single mandatory frequency in Irish or EU regulations, but annual thermographic surveys of critical switchgear are considered good practice. Insurance companies increasingly request evidence of routine thermal surveys. The Health and Safety Authority (HSA) guidance on maintaining electrical installations supports a risk-based approach to inspection intervals. IEC 60364-6 (low-voltage electrical installations, verification) and the ETCI National Rules both reference the need for periodic verification, within which thermography is a widely accepted tool.
Beyond electrical work: building surveys, industrial, and safety applications
Thermal imaging extends well beyond electrical panels. In building energy surveys, it reveals missing or damaged insulation, air leakage paths, thermal bridging, and moisture ingress. For industrial plant, it monitors steam traps, refractory linings, bearings, and process piping.
Emergency services use thermal cameras to locate people in smoke-filled buildings and to identify fire hot spots behind walls. Maritime and security applications rely on the technology's ability to produce a clear image in total darkness and through fog. Anywhere you need to see heat, rather than light, thermal imaging has a role.
Training and certification for thermographers
Owning a thermal camera does not make you a qualified thermographer. Interpreting thermograms accurately requires an understanding of emissivity, reflected temperature, atmospheric conditions, spatial resolution, and the specific failure modes you are looking for. Misinterpreting a hot spot, or missing one entirely, can have serious consequences.
Thermographer certification typically follows a tiered structure (Level 1, Level 2, Level 3) based on ISO 18436-7 and ISO 9712 (previously EN 473). Level 1 covers data collection and basic analysis; Level 2 covers report writing and advanced diagnostics; Level 3 covers programme management. Powerpoint Engineering offers thermal imaging training courses designed for electrical and maintenance professionals working in Irish industry.
FAQs
Can a thermal imaging camera see through walls?
No. Thermal cameras image surface temperatures only. If a heat source behind a wall warms the surface enough, the camera may detect that temperature difference, but it is reading the wall surface, not seeing through it. Solid materials block infrared radiation.
What accuracy can I expect from a professional thermal camera?
Most professional uncooled cameras are accurate to ±2 °C or ±2% of the reading, whichever is greater. Accuracy depends on correct emissivity settings, distance to the target, and atmospheric conditions. Using incorrect emissivity on a reflective surface is the most common source of significant error.
Do I need training before using a thermal camera for electrical inspections?
Strictly speaking, there is no legal requirement in Ireland to hold a specific certification. However, misinterpreting thermal data can lead to missed faults or unnecessary shutdowns. Professional training to at least Level 1 (ISO 18436-7) is strongly recommended and increasingly expected by insurers and facility managers.
Getting started with thermal imaging
Whether you need a camera, a calibrated rental unit, or a full thermographic survey carried out by experienced personnel, Powerpoint Engineering can help. We distribute FLIR and Fluke thermal imagers, run thermal imaging training courses, and carry out on-site surveys across Ireland. If you are considering adding thermography to your maintenance programme, speak to our team for practical, no-obligation advice.