Ultimate Infrared Thermography Glossary

200 Abbreviations & terminology every thermographer needs to know

Author picture

Marcus Huang
Level-2 Infrared Thermographer
Certified Adult Educator (ACLP)

Updated on November 2025

Entering the world of Infrared Thermography is like gaining a brand-new vision. If you want to truly “see the unseen,” you must first learn to speak the language of heat.

But if all the technical terms — emissivity, delta-T, thermograms — are making your head spin faster than an overloaded motor, don’t worry. The Institute of Infrared Thermography is here to help you stay ‘cool’.

To boost your thermal literacy, we’ve compiled a handy Thermography Terminology Guide that you can read, reference, and share. Bookmark it, and revisit anytime you encounter a confusing term or acronym during your infrared inspection journey.

Quick definitions of top infrared thermography terms

  1. Blackbody: An ideal object (emissivity ε = 1) that absorbs all radiation and only emits heat based on its own temperature.
  2. Emissivity (e): The ratio of infrared radiation emitted by an object compared to that of a perfect blackbody. Values range from 0 to 1 and depend on surface properties, material, and temperature.
  3. Hotspot: An area in a thermogram that appears hotter than its surroundings, showing temperature contrast.
  4. Quantitative Analysis: An analysis method focused on assigning numerical temperature values or radiant energy levels to objects or processes for precise evaluation.
  5. Thermogram: An infrared image produced by a thermal imager that displays surface temperature distributions, with different colors or grayscale tones representing different temperature values.

common infrared thermography terms to improve your thermal inspections

A B C D E F G H I J K L M N O P Q R S T U V W Z

1.  Absolute Temperature Scale
  • Definition: A temperature measurement scale based on the coldest possible temperature equal to zero (typically in Rankine or Kelvin).
  • i.e. A scale that starts from the coldest temperature possible (absolute zero).
  • Note: Use Kelvin for heat formulas to ensure accurate calculations.
2. Absolute Zero
  • Definition: Absolute zero is -273.15 °C (0 Kelvin = -459.69 °F). All bodies at this temperature emit no infrared radiation.
  • i.e. The coldest anything can ever get — no heat, no movement.
  • Note: All objects above this temperature give off infrared radiation.
3. Absorption
  • Definition: When infrared radiation hits an object, part of the energy is absorbed, making the object warmer.
  • i.e. An object takes in heat and gets warmer.
  • Note: Dark, rough surfaces absorb more infrared energy than shiny ones.
4. Absorptivity
  • Definition:  The fraction of radiant energy absorbed by a material’s surface. For a blackbody, absorptivity = 1.0.
  • i.e. How much heat a surface “soaks in.”
  • Note: If an object’s absorptivity is high, its reflectivity and transmissivity are low. Reference Formula: A.R.T. = 1 (A is absorptivity, R is reflectivity, T is transmissivity).
5. Accuracy
  • Definition: A measure of how close the thermal finding is to the actual value.
  • i.e. How close your measurement is to the real answer.
  • Note:  Accuracy depends on proper calibration, surrounding conditions, and how a thermal image is captured.
6. Active Thermography
  • Definition: A technique where an external energy source is intentionally used to heat or cool a target to observe thermal responses.
  • i.e. Adding extra heat or cooling to see hidden problems.
  • Note: Typically applied in building inspections (e.g. detecting moisture under roofs/walls) or material testing (e.g., finding cracks, delaminations, or voids).
7. Anomaly (Thermal)
  • Definition: A temperature variation that differs significantly from the expected or normal baseline in a thermal image.
  • i.e. Any unusual heat pattern that may indicate potential issues.
  • Note: An anomaly is not always a defect, but it signals the need for further investigation.
8. Ambient Temperature
  • Definition: Temperature of the air around the target or the instrument.
  • i.e. Surrounding air temperature.
  • Note: Ambient temperature is more crucial in building and mechanical inspections, as it directly affects heat flow and fault detection.
9. Apparent Temperature
  • Definition: The temperature reading shown by the imager before corrections for emissivity, reflection, or atmosphere.
  • i.e. What the camera “thinks” the temperature is, before adjustments.
  • Note: Adjust for emissivity and reflection to ensure accurate reading.
10. A + R + T = 1
  • Definition: A law of energy conservation stating that for any material, the fraction of infrared radiation Absorbed, Reflected, and Transmitted must always add up to 1 (100%).
  • i.e.  All heat energy hitting an object is either taken in, bounced back, or passed through, nothing is lost.
  • Note: More Absorptivity = less Reflectivity & Transmissivity (and vice versa, always adds to 1). 
11. ASTM
  • Definition: American Society for Testing and Materials.
  • i.e. Professional organisation establishing official test standards for materials, products, systems, and services across many industries.
  • Note: ASTM standards are one of the main references thermographers rely on for inspection and reporting.
12. ASNT
  • Definition: American Society for Nondestructive Testing.
  • i.e. Professional organisation that supports and certifies professionals in NDT (nondestructive testing).
  • Note: ASNT publishes widely used personnel qualification & certification guidelines (e.g., SNT-TC-1A, CP-105, CP-189) that many employers reference for infrared inspections, training and certification.
13. Auto Image Adjust
  • Definition: An automatic camera function that adjusts Level and Span based on image content.
  • i.e. Camera shortcut that auto-sets brightness and contrast for you.
  • Note: Handy for quick scans, but thermographers often switch to manual adjustment for accurate reporting.

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14. Background Temperature
  • Definition: The temperature of objects reflected by the target.
  • i.e. Also known as reflections.
  • Note: Occurs on shiny surfaces, can make them look hot or cold, even when they’re not.
15. Baseline Data
  • Definition: Thermal data collected when a component is in optimum operating condition.
  • i.e. The “healthy” temperature used as a reference point for future inspections.
  • Note: Potential anomalies detected shall be compared back to it.
16. Blackbody
  • Definition: An ideal object (emissivity ε = 1) that absorbs all radiation and only emits heat based on its own temperature.
  • i.e. Completely non-reflective object.
  • Note: Blackbody theory is the basis for how infrared cameras are calibrated.
17. Blackbody Calibration Source
  • Definition: A reference heat source with stable temperature and emissivity.
  • i.e. Device used to check and calibrate infrared cameras.
  • Note: Most standards require calibration checks at yearly intervals, to keep results reliable.
18. Building Envelope
  • Definition: The exterior system separating indoor from outdoor environments (walls, glazing, joints, insulation).
  • i.e. Building facade.
  • Note: Infrared thermography enhances Periodic Facade Inspections (PFI) for moisture, delamination, and air-leak detection.

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19. Calibration Check
  • Definition: A formal check of the radiometric accuracy of the imaging system performed by comparing its measured value to that of a known reference source, typically a blackbody device.
  • i.e. A check to see if your camera measures heat accurately.
  • Note: Attach calibration certificates in infrared reports.
20. Cavity Effect
  • Definition: When infrared radiation enters a recessed area (like a hole or slot) and reflects multiple times within it, the trapped energy raises the area’s effective emissivity, making it behave almost like a blackbody surface.
  • i.e. When heat enters a deep hole or slot, it bounces around and gets trapped — making that cavity appear as a strong, high-emissivity heat source in the thermal image.
  • Note: Aim your thermal camera slightly off-axis or use the cavity’s inner surface for readings — it gives a more accurate temperature and reduces reflection error.
21. Celsius (°C)
  • Definition: A temperature unit where 0°C is the freezing point of water and 100°C is the boiling point at normal pressure.
  • i.e. Temperature scale built around water’s behavior.
  • Note: Standard unit used in thermal inspections.
22. Certification
  • Definition: Official validation by a recognised institute of a thermographer’s knowledge and skills, assessed against predetermined standards.
  • i.e. Verified acknowledgment of theoretical and practical competency.
  • Note:  ID badge or relevant credentials shall be displayed when conducting thermal inspections.
23. Certified Thermographer
  • Definition: A trained professional who has officially fulfilled the qualification requirements stipulated by a recognised infrared thermography institution.
  • i.e. A thermographer officially trained to perform relevant thermography tasks.
  • Note: Thermography tasks permitted follows the respective certification level (e.g. Level 1, 2, or 3).
24. Coldspot
  • Definition: An area in a thermogram that appears cooler than its surroundings, showing temperature contrast.
  • i.e. The coldest areas in a thermal image.
  • Note: In building inspections, a coldspot may indicate moisture; in electrical systems, it may indicate equipment failure or equipment not switched on.
25. Colour Palette
  • Definition: The selection of colour schemes used to display thermal images (e.g., rainbow, iron, grayscale).
  • i.e. The “colour filter” that shows heat differences more clearly.
  • Note: Different palettes do not change the data, only how it looks. Use it to highlight contrasts and make the image easier to interpret.
26. Comparative Analysis
  • Definition: A diagnostic method that compares thermal patterns across similar components to detect abnormal differences.
  • i.e. Checking “same parts” side by side to see which one looks different.
  • Note: This method should only be used when components are under the same load or conditions.
27. Condition-Based Maintenance
  • Definition: A proactive maintenance strategy that uses real-time monitoring of an asset’s actual condition to determine the optimal time for maintenance, preventing failures before they occur.
  • i.e. Performing maintenance only when an anomaly is detected.
  • Note: In thermography, this typically means scheduling rectification according to the Thermographer’s recommended Severity Criteria.
28. Conduction
  • Definition: Heat transfer within solid materials, where energy moves from an area of higher to lower temperature (warmer to colder regions).
  • i.e.  Heat flowing through a solid object.
  • Note: In thermography, conduction can reveal insulation defects, loose electrical connections, or heat transfer along structural/electrical paths.
29. Conductivity
  • Definition: A material property that measures how easily heat flows through it by conduction under a temperature difference.
  • i.e. How fast heat moves through a material.
  • Note: Materials with high conductivity (like metals) transfer heat quickly, while low-conductivity materials (like insulation) help prevent heat loss.
30. Contact Resistance
  • Definition: The electrical resistance at the interface between two conductive surfaces, typically caused by oxidation, dirt, or inadequate pressure at the joint.
  • i.e. The gap between metal contacts that makes electricity flow harder and generates heat.
  • Note: To prevent further hotspot formation, isolate power and reterminate accordingly. High contact resistance may arc unexpectedly.
31. Continuous Adjust
  • Definition: A camera function that automatically and continually adjusts brightness and contrast based on image content.
  • i.e.  Auto-tuning the image as you move the camera.
  • Note: Use Continuous Adjust function for quick focusing, use manual adjustment for detailed inspections.
32. Contrast Enhancement
  • Definition:  Image processing techniques (e.g., span/level adjustment, histogram equalization) used to highlight subtle temperature differences in low-contrast thermal scenes.
  • i.e. Makes heat differences easier to see.
  • Note: Enhances visibility but may exaggerate real temperature gradients.
33. Convection
  • Definition: Heat transfer within liquids or gases, where energy moves from an area of higer to lower temperature (warmer to colder regions).
  • i.e. Heat moving as air or liquid flows.
  • Note: In thermography, convection can reveal blocked, leaking HVAC ducts, or poor insulation in buildings.

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34. Delta-T (ΔT)
  • Definition: A traditional method in thermography used to identify faults by comparing the temperature difference between two points, such as between a target and ambient temperature or between similar components under the same conditions.
  • i.e. Checking if one spot is hotter or colder than another.
  • Note: In electrical thermal inspections, loads are rarely identical. Replying solely on ΔT method may limit reading accuracy. See F.A.S.T. Check Method.
35. Depth Of Field (DOF)
  • Definition: The distance range in an image that appears acceptably in focus, extending in front of and behind the point of focus.
  • i.e. Distance between the closest and farthest objects in a photo that remains sharp.
  • Note: Keep some distance from the target. Taking the thermal image too close may cause parts to appear blurry.
36. Depth Of Focus 

The range of motion of the focus assembly around a set focus distance which will not defocus an object at that focus distance (image space distance)

  • Definition: The space between the lens and the image sensor where the image will appear in focus to the human eye.
  • i.e. How much the lens can move while the image stays sharp.
  • Note: Use fine focusing adjustments to keep thermal readings accurate.
37. Detector
  • Definition: A sensor that captures infrared radiation and converts it into an electrical signal. Its performance is defined by geometric resolution (pixels) and thermal resolution (NETD).
  • i.e. The part of the camera that “sees” heat and turns it into an image.
  • Note: Higher pixel count improves image detail, while lower NETD values improve sensitivity to small temperature differences.
38. Display Resolution
  • Definition: The smallest temperature change a thermal imager can show on its display, usually expressed in degrees, tenths, or hundredths of a degree.
  • i.e. How finely the screen can show temperature differences.
  • Note: Higher display resolution allows clearer readings

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39. Electromagnetic Radiation
  • Definition: Energy released when charged particles accelerate, producing waves such as radio, infrared, visible light, X-rays, and more depending on frequency.
  • i.e.  Invisible and visible energy waves, like heat, light, or radio signals.
  • Note: Infrared thermography relies on one part of this spectrum, infrared radiation, to detect heat patterns.
40. Electromagnetic Spectrum
  • Definition: The full range of electromagnetic radiation, arranged by wavelength and frequency, from very long waves (radio) to very short waves (gamma rays).
  • i.e. The “map” of all energy waves.
  • Note: Infrared occupies a small band of this spectrum (0.7–100 µm).
41. Emissivity (e)
  • Definition: The ratio of infrared radiation emitted by an object compared to that of a perfect blackbody. Values range from 0 to 1 and depend on surface properties, material, and temperature.
  • i.e. How much heat a surface gives off, closely related to how much it can absorb.
  • Note: For most electrical inspections, a standard emissivity setting of 0.95 is commonly used for reliable results.
42. Equilibrium
  • Definition: A condition where temperatures have stabilized and no further heat transfer occurs between objects.
  • i.e. When equipment or a surface has settled to a steady temperature before inspection.
  • Note: In thermography, readings should be taken only after thermal equilibrium is reached for accuracy.
43. Error Sources
  • Definition: Factors that introduce bias or uncertainty into thermal images or radiometric temperature readings.
  • i.e. False anomalies that affect thermal measurement accuracy.
  • Note: Common error source include reflections from polished copper busbars. Change viewing angle or use emissivity tape.
44. External Thermal Loading
  • Definition: A technique that applies external heat or cooling sources to create temperature differences that make defects more visible.
  • i.e. Adding heat from outside to spot hidden problems.
  • Note: Commonly used in building inspections (e.g., roofs, walls, facades) when natural temperature contrast is insufficient to reveal faults.

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45. Fahrenheit (°F)
  • Definition: A temperature unit where 32°F is the freezing point of water and 212°F is the boiling point at normal pressure.
  • i.e. Temperature scale mainly used in North America.
  • Note: Conversion to Celsius is often needed in thermography (°F = °C × 1.8 + 32).
46. Far Infrared (FIR)
  • Definition: Longest-wavelength portion of the infrared spectrum, characterised by wavelengths from approximately 15 to 1,000 micrometers (μm).
  • i.e. The “far end” of heat waves, beyond what most thermal cameras detect.
  • Note: In practice, thermography mainly uses the Long-Wave Infrared (LWIR) band (8–14 µm).
47. F.A.S.T. Check Method
  • Definition: A structured 4-Step thermal scanning workflow introduced by the Institute of Infrared Thermography (IIRT), designed to deliver quick, simple and precise inspections.
  • i.e. Combines visual observation, thermal assessment, and structured reporting into one process.
  • Note: Can be used in all electrical inspections under any conditions or environments.
48. Field Of View (FOV)
  • Definition: The horizontal and vertical angle a thermal imager can capture, expressed in degrees (e.g. 32°).
  • i.e. How much of the scene the camera can “see.”
  • Note: Wide FOV (e.g. 50°~60°) is useful for scanning large areas, while narrow FOV (e.g. 6°~15°) provides better detail for small or distant targets.
49. Focal Plane Array (FPA)
  • Definition: A type of infrared detector made of many tiny sensors (bolometers) arranged in a grid, used in thermal cameras to capture heat as an image.
  • i.e. The “sensor grid” that turns heat into a picture.
  • Note: Typical resolution is 320×240 pixels, while high-end cameras use 640×480 pixels for the best detail.
50. Focal Point
  • Definition: The point at which the infrared camera focuses the target onto its detector, producing the smallest measurable spot size.
  • i.e. The exact point where the image is sharpest.
  • Note: Knowing the focal point is critical — being out of focus increases spot size and reduces measurement accuracy.
51. Four-T Framework
  • Definition: A structured methodology developed by the Institute of Infrared Thermography (IIRT), defines the 4 core foundation pillars every practising thermographer must understand: Temperature, Tool, Target, and Technique.
  • i.e. A simplified framework to master infrared science, thermal camera operations, material temperature tolerance, and effective inspection methods.
  • Note: Required competency for certified thermographers.

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52. Germanium (Ge)
  • Definition: A semiconductor material commonly used in infrared optics because it is highly transparent to infrared radiation in the 2–14 µm range.
  • i.e. A special glass that lets heat energy pass through so cameras can see it.
  • Note: Most infrared camera lenses and windows are made of germanium, as normal glass blocks infrared radiation.
53. Graybody
  • Definition: An object whose emissivity is a constant value less than 1 across all wavelengths.
  • i.e. A surface that gives off most, but not all, of the heat (e.g. 0.9).
  • Note: Measuring a painted metal surface (graybody) gives more accurate readings than shiny bare metal.

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54. Heat Transfer
  • Definition: The flow of thermal energy from one point to another, occurring through conduction, convection, or radiation.
  • i.e. How heat moves from hot areas to cold areas.
  • Note: Understanding heat transfer fundamentals is essential for analysing anomalies accurately.
55. Hertz [Hz]
  • Definition: The number of frames a thermal camera captures per second (image refresh rate). Higher rates produce smoother motion and are preferred for video or fast-moving targets.
  • i.e. How many thermal pictures the camera takes every second.
  • Note: 30~60 Hz is suitable for moving equipment, 9 Hz is suitable for static inspections.
56. Herschel, Sir William
  • Definition: The scientist who discovered infrared radiation in 1800 while experimenting with sunlight and prisms.
  • i.e. The person who first found heat beyond visible light.
  • Note: His discovery laid the foundation for modern infrared thermography.
57. Histogram Equalisation
  • Definition: An image-processing technique that automatically adjusts contrast by redistributing temperature levels more evenly across the thermal image.
  • i.e. A tool that makes hidden heat patterns easier to see.
  • Note: Useful for revealing details in low-contrast images, but overuse can distort true temperature gradients.
58. Hotspot
  • Definition: An area in a thermogram that appears hotter than its surroundings, showing temperature contrast.
  • i.e.  The hottest areas in a thermal image.
  • Note: In electrical inspections, a hotspot may indicate overload or loose connections; in mechanical systems, it may indicate friction or failing components.

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59. Image Fusion
  • Definition: A visual overlay tool that combines thermal and visible images into one, aligning heat patterns with real-world visuals.
  • i.e. Blends thermal and digital photos.
  • Note: Useful for reports and documentation, helps identify exact defect locations clearly.
60. Infrared (IR)
  • Definition: Non-visible electromagnetic radiation in the band from 0.7 µm to 100 µm, located between visible light and microwaves.
  • i.e. Invisible heat energy to the human eye, only seen with an infrared camera.
  • Note: All objects above absolute zero (-273.15 °C) emit infrared radiation.
61. Infrared Camera
  • Definition: An optical–electrical device that converts infrared radiation into a visible image (thermogram) displayed on a screen. Typically operates in the 3–5 µm or 7–14 µm ranges, suitable for detecting heat from everyday objects.
  • i.e. A device that makes invisible heat visible.
  • Note: For everyday maintenance inspections, the most common type is the Long-Wave Infrared (LWIR) camera, operating in the 7–14 µm range.
62. Infrared Thermometer
  • Definition: An instrument that converts infrared radiation from a single spot on a surface into a temperature reading, guided by a laser pointer for aiming.
  • i.e. Also known as a spot thermometer (or handheld IR thermometer).
  • Note: Commonly used for quick spot checks, providing only a single-point temperature reading without imaging.
63. Infrared Report
  • Definition: A formal document that records the findings of a thermal imaging inspection, including key parameters, images, temperature data, analysis, and recommendations.
  • i.e. A report that shows heat problems and suggests what to do next.
  • Note: Report templates should comply with recognised international thermography standards and best industry practices.
64. Infrared Thermography
  • Definition: The science of detecting and analysing objects based on the thermal radiation they emit, using specialised infrared cameras.
  • i.e. A technique that makes heat patterns visible for inspection and analysis.
  • Note: Widely applied in electrical, mechanical, and building maintenance, and should follow international standards for accurate and reliable results.
65. Infrared Thermographer
  • Definition: A proficient individual who is trained and qualified to use infrared thermal imaging cameras, possessing relevant subject matter expertise (e.g. M&E, Building etc).
  • i.e. A practitioner officially trained to conduct thermal assessments.
  • Note: Under Singapore Standards, an Infrared Thermographer is required to be at least Level-1 Certified to perform thermographic inspections.
66. Infrared Window
  • Definition: An optical element that allows infrared radiation to pass through while blocking other wavelengths, enabling thermal inspection without opening equipment enclosures.
  • i.e. A special “viewing window” that lets a thermal camera see inside live equipment safely.
  • Note: Commonly installed on electrical panels with dangerous voltages to protect technicians during inspections.
67. Installation Faults
  • Definition: Errors made during electrical system setup, such as using undersized conductors, poor crimping, improper lug termination, or incorrect torque, leading to uneven current flow and overheating.
  • i.e. Defects when wiring or connecting components that cause resistance and heat buildup during operation.
  • Note: Check torque, conductor size, and termination quality. Improper installation often mimics loose or high-resistance faults on thermal images.
68. Insulation Faults
  • Definition: Defects in electrical insulation that allow current leakage, partial discharge, or arcing between conductors or to ground, often caused by ageing, contamination, or moisture.
  • i.e. When insulation breaks down, electricity leaks or arcs where it shouldn’t, creating heat and damage.
  • Note: Typically seen as irregular hotspots or heat spread.
69. IFOV (Instantaneous Field Of View)
  • Definition: A specification of an infrared camera’s spatial resolution, given in mrad (milliradian), showing the smallest object size a single pixel can detect at a given distance.
  • i.e. The size of what one pixel “sees.”
  • Note: Telephoto lens have low IFOV (e.g. 1 mrad), ideal for small or distant targets. Wide-angle lens have high IFOV (e.g. 3 mrad), suited for scanning large areas.
70. Isotherm
  • Definition: An image analysis function that highlights areas of equal or specified temperature range, displayed as colored zones or contour lines.
  • i.e. Shows all areas hotter (or colder) than a set temperature limit.
  • Note: Useful for quickly spotting overheating components, cold spots, or moisture by setting threshold temperatures.

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71. Joule
  • Definition: The standard unit of thermal energy. In thermography, it is how much heat energy is absorbed, released, or transferred by a material.
  • i.e. A basic unit for measuring energy or heat.
  • Note: 1 joule per second (1 J/s) = 1 watt (W) of heat. This helps quantify how much energy a hotspot is releasing.
72. Junction Heating
  • Definition: Heat generated at electrical connections due to resistance from loose contacts, corrosion, or excessive current flow.
  • i.e. Extra heat building up where wires or terminals connect.
  • Note: A common finding in electrical thermography, as hotspots at junctions often signal faults requiring corrective action.

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73. Kelvin (K)
  • Definition: A temperature unit starting at absolute zero (−273.15 °C), where 0 K represents the complete absence of heat.
  • i.e. Temperature scale that begins at the coldest possible point.
  • Note: Commonly used in scientific and engineering formulas for heat and energy calculations.
74. Kinetic Energy
  • Definition: The energy an object possesses due to its motion.
  • i.e. Moving things carry energy (like a rolling ball).
  • Note: In thermography, higher kinetic energy of particles at higher temperatures results in stronger infrared radiation.
75. Kirchoff’s Law
  • Definition:

    In thermal equilibrium, the absorptivity of an opaque surface is equal to its emissivity (a = e).

  • i.e. A surface that absorbs heat well also emits heat equally well.

  • Note: Helps thermographers link absorption to emission—key when estimating emissivity values during inspections.

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76. Lambert Radiator
  • Definition: An object that reflects incoming radiation equally in all directions, providing uniform diffusion.
  • i.e. A surface that scatters reflected heat evenly, like a perfectly matte mirror for infrared.
  • Note: Used as a reference surface to measure reflected temperature in thermography.
77. Laser Pointer / Marker
  • Definition: A camera feature that projects a thin, concentrated laser beam to mark specific parts of the object being inspected.
  • i.e. A built-in laser pointer that shows exactly where the camera is measuring.
  • Note: Serves as a guide, useful for pinpointing inspection spots, especially in hard-to-reach or cluttered areas.
78. Laser Pyrometer
  • Definition: An instrument that converts infrared radiation from a single spot on a surface into a temperature reading, guided by a laser pointer for aiming.
  • i.e. Also known as a spot thermometer (or handheld IR thermometer).
  • Note: Commonly used for quick spot checks, providing only a single-point temperature reading without imaging.
79. Latent Heat
  • Definition: Heat energy used when a material changes state (like melting or boiling) without its temperature changing.
  • i.e. The hidden heat that melts ice into water or turns water into steam.
  • Note: In thermal inspections, latent heat can make areas look colder or hotter (e.g., damp spots from evaporation).
80. Lenses
  • Definition: Optical components that determine the field of view (FOV) of a thermal imager and the size of the measurement spot.
  • i.e. Wide lenses show a large area, telephoto lenses zoom in on small details from far away.
  • Note: Use wide-angle lenses (e.g. 32°) for scanning large surfaces, and telephoto/super-telephoto lenses (e.g. 9°) for precise inspection of small or distant targets.
81. Level
  • Definition: The midpoint of the temperature scale used in a thermal image display.
  • i.e. The “center” temperature around which the image colors are adjusted.
  • Note: Setting the right level ensures the thermal image is not too dark or too bright, making hot or cold spots easier to detect.
82. Linear Array
  • Definition: A sensor made up of infrared detector elements arranged in a single straight line, equally spaced apart.
  • i.e. Like a row of thermal “pixels” that scan one line at a time.
  • Note: Commonly used in line-scan infrared systems for inspecting moving materials such as conveyor belts, sheets, or rotating equipment.
83. Line Scan Rate
  • Definition: A camera specification that states how many lines per second an infrared scanner or imager records.
  • i.e. How fast the system “draws” lines of heat to form an image.
  • Note: For M&E use, higher scan rates are important when monitoring fast-moving belts, rotating motors, or turbines.
84. Line Scanner
  • Definition: A thermal device that scans heat along a single line of a target and builds a full image as the object moves.
  • i.e. Captures heat patterns one line at a time.
  • Note: Often used in moving processes such as conveyor belts, rotating drums, or sheet materials where the motion completes the thermal picture.
85. Long-Wave Infrared (LWIR)
  • Definition: A portion of the infrared spectrum with wavelengths from approximately 8 to 14 micrometers (µm).
  • i.e. The heat band most everyday thermal cameras are built to detect.
  • Note: LWIR is the primary band used in maintenance thermography.
86. Loose Termination
  • Definition: Inadequate mechanical tightness at lugs or studs that increases contact resistance and localised heating under load.
  • i.e. A loose wire or bolt that doesn’t make full contact, causing heat build-up when current flows.
  • Note: Always de-energise before tightening, never torque live connections.
87. Luminance
  • Definition: The brightness level of a colour on a thermal image display, based on how the human eye perceives it.
  • i.e. How bright or dim a colour looks on the screen.
  • Note: Managed indirectly by choosing different colour palettes, level/span settings, or screen brightness to make images easier to interpret.

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88. Manual Adjust
  • Definition: A camera function that allows the user to manually set image parameters such as level, span, and contrast.
  • i.e. Manually fine-tuning the image instead of letting the camera auto-adjust.
  • Note: Essential for accurate thermography reporting, as auto settings may hide or exaggerate anomalies.
89. Medium
  • Definition: The material or space (air, vacuum, liquid, or solid) that infrared radiation passes through between the target and the measuring instrument.
  • i.e. What’s in between an object and the camera, like air, glass, or water.
  • Note: The medium can affect accuracy, e.g., moisture, dust, or glass may absorb or block infrared radiation.
90. MCT (Mercury Cadmium Telluride)
  • Definition: A semiconductor material [HgCdTe] used in infrared detectors that provides very fast and highly sensitive response, but requires cooling to operate effectively.
  • i.e. A special material that makes high-performance IR cameras more sensitive, but only when cooled.
  • Note: Commonly used in scientific or military-grade infrared systems, not in everyday maintenance thermography (which usually uses uncooled microbolometers).
91. Micro-Cooler
  • Definition: A compact cooling device, often using the Stirling cycle, that chills an infrared detector or focal plane array down to about liquid nitrogen temperature (77 K).
  • i.e. A tiny machine that keeps special infrared sensors very cold so they work properly.
  • Note: Essential for cooled infrared cameras (like MCT [HgCdTe] systems) to achieve high sensitivity, but not used in standard uncooled maintenance cameras.
92. Micron (µm)
  • Definition: A unit of length equal to one millionth of a meter, commonly used to describe infrared wavelengths.
  • i.e. A tiny unit to measure heat waves (1,000,000 microns = 1 meter)
  • Note: Infrared thermography typically measures in the 0.7–14 µm range, with most thermal cameras working in the 8–14 µm band.
93. Milliradian [MRAD]
  • Definition: A unit of angular measurement equal to one-thousandth of a radian (0.057°), often used to specify the field of view or resolution of infrared cameras.
  • i.e. A very small angle used to describe how fine a camera can “see.”
  • Note: Smaller mrad values mean higher resolution, useful for detecting small faults at longer distances.
94. Minimum Focus Distance (MFD)
  • Definition: Closest distance at which the lens can focus accurately.
  • i.e. Anything closer than this distance will be out of focus.
  • Note: Use macro or close-up lenses for small components.
95. Moisture Ingress
  • Definition: Water penetration into building or equipment assemblies (facades, roofs, walls, insulation, joints), driving heat-flow changes and material degradation.
  • i.e. Trapped dampness appearing as cool patches on infrared.
  • Note: Perform facade infrared inspections in calm, dry weather; avoid rain and note the most recent sun or rain exposure.
96. MRTD (Minimum Resolvable Temperature Difference)
  • Definition: A performance test that determines the smallest temperature difference a thermal imager can distinguish under controlled conditions, accounting for optics, detector, display, and operator interpretation.
  • i.e. How fine a heat difference the entire camera system can actually show in practice.
  • Note: MRTD is generally not listed on datasheets, but a lower NETD specification usually indicates better MRTD performance, helping cameras reveal subtle faults more clearly.
97. Modulation
  • Definition: In thermal imaging, modulation refers to the contrast of an image, calculated as the difference between the maximum and minimum luminance, divided by their sum (Lmax – Lmin)/(Lmax + Lmin).
  • i.e. How strong the contrast looks between the hottest and coldest areas in a thermal image.
  • Note:Higher modulation means clearer images, making it easier to spot small or faint anomalies.
98. MTF (Modulation Transfer Function)
  • Definition: A test that measures how well an imaging system can reproduce detail from a target, showing how resolution changes with distance and spatial frequency.
  • i.e. How clearly the camera can show fine details as objects get smaller or farther away.
  • Note: MTF is generally not listed on datasheets, but cameras with higher resolution and quality optics usually have better MTF performance, resulting in sharper images and clearer fault detection.
99. MWIR (Mid-Wavelength Infrared)
  • Definition: A portion of the infrared spectrum with wavelengths from approximately 3 to 5 micrometers (µm).
  • i.e. The “mid-band” of heat waves, detected by specialised cooled thermal cameras.
  • Note: MWIR is mainly used in high-performance or scientific applications (e.g. gas detection, aerospace, or research).

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100. NIR (Near Infrared)
  • Definition: The shortest-wavelength portion of the infrared spectrum, ranging from approximately 0.7 to 1.4 micrometers (µm).
  • i.e. Just beyond visible red light, invisible to the eye but still infrared.
  • Note: NIR is commonly used in optical sensors, fiber optics, and night vision, not commonly used in maintenance thermography.
101. Neutral Density Filter
  • Definition: An optical filter that reduces infrared radiation evenly across a wide range of wavelengths, often used to extend the measurable temperature range of a thermal camera.
  • i.e. A filter fitted to a thermal camera so very hot targets can be measured without saturating the detector.
  • Note: Useful in applications like furnaces, kilns, or molten metal inspections where temperatures exceed the normal camera range (often >650 °C to 2000 °C).
102. NETD (Noise Equivalent Temperature Difference)
  • Definition: A specification, expressed in millikelvin (mK), that indicates the smallest temperature difference a thermal camera can detect above its own noise level. It is the key measure of a camera’s thermal sensitivity.
  • i.e. The tiniest heat change a thermal camera is sensitive enough to pick up.
  • Note: Typical modern cameras have a NETD of about 30–50 mK; lower values provide clearer images and make it easier to spot subtle faults.
103. Noise
  • Definition: Unwanted disturbances or interference in an infrared image, caused by sensor electronics or signal crosstalk, that reduce image clarity.
  • i.e. Static or graininess in a thermal image that hides fine details.
  • Note: Reduce noise by using a thermal camera with low NETD (higher sensitivity).
104. NDT (Non-Destructive Testing)
  • Definition: An inspection method that evaluates materials or components for defects without causing damage or altering their function.
  • i.e. Checking equipment for problems without breaking or taking it apart.
  • Note: Infrared thermography is a common NDT inspection method since it is non-contact.
105. Non-Gray Body
  • Definition: An object whose emissivity changes with wavelength, meaning its radiation pattern is not uniform across the spectrum. Also called a “colored body” or “real body.”
  • i.e. Materials like glass or plastic films that don’t give off heat evenly across all infrared wavelengths.
  • Note: Always verify emissivity settings when inspecting non-gray bodies to avoid inaccurate readings.
106. NUC (Non-Uniformity Correction)

  • Definition: A periodic calibration process in thermal cameras that adjusts each detector pixel individually to correct for fixed pattern noise and ensure uniform image quality.

  • i.e. A camera correction that keeps thermal images accurate and consistent across all pixels.

  • Note: Most cameras run NUC automatically to maintain accuracy during inspections.

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107. Objective Lens

  • Definition: The primary lens of an infrared camera that gathers infrared radiation from the target and defines the system’s total field of view.

  • i.e. The main lens that lets the camera “see” heat, setting how wide or narrow the image appears.

  • Note: Often interchangeable to suit different applications, such as wide-angle for large areas or telephoto for distant/small targets.

108. Object Parameters

  • Definition: The set of values that describe both the object and the conditions under which its temperature is measured, such as emissivity, ambient temperature, reflected temperature, and distance.

  • i.e. The measurement settings that tell the camera how to read the object correctly.

  • Note: Entering accurate object parameters is critical for precise temperature readings in thermography.

109. Object Signal

  • Definition: A non-calibrated value representing the infrared radiation received by the camera from an object.

  • i.e. The first “heat data” the camera picks up before corrections are applied.

  • Note: Not an actual temperature yet, the infrared camera must process this signal to turn it into a correct reading.

110. Ohmmeter
  • Definition: An instrument used to measure the electrical resistance of a component or circuit, expressed in ohms (Ω).
  • i.e. A tool that tells how strongly a material or device resists the flow of electricity.
  • Note: Useful in thermography as a supporting tool to confirm electrical faults indicated by hotspots.
111. Opaque
  • Definition: A material property where no thermal infrared energy passes through (transmissivity = 0). In thermography, an opaque surface blocks all incident radiation.
  • i.e. A material that completely stops heat from passing through it.
  • Note: Most inspection materials (e.g. painted metal, electrical busbars, switchgear covers, cable insulation) are opaque in the infrared range, so cameras only measure surface radiation, not what’s behind.
112. Operating Temperature Range
  • Definition: The range of ambient temperatures within which a thermal camera or system can function accurately and reliably. Limits may be set by calibration, detector cooling ability, or hardware tolerances.
  • i.e. The safe temperature range where the camera works properly without errors.
  • Note: Staying within the specified camera operating range ensures accurate readings.
113. Optical Element
  • Definition: A component in an infrared instrument that collects, transmits, restricts, or reflects infrared energy as part of the sensing or imaging process.
  • i.e. Any part, like a lens or filter, that helps control how heat energy reaches the detector.
  • Note: Common infrared optical elements include germanium lenses, protective windows, and filters, each chosen for specific inspection needs.
114. Optics
  • Definition: The infrared lens system of a thermal camera, typically made of germanium or chalcogenide glass, that focuses infrared radiation onto the detector. It directly affects Field Of View (FOV), spatial resolution (IFOV), and spectral response.
  • i.e. The special lens that lets the camera “see” heat and focus it into a clear thermal image.
  • Note: Normal glass blocks infrared and cannot be used; instead, germanium or chalcogenide are required. 

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115. Palette
  • Definition: The set of colours applied to a thermal image to represent temperature differences, without changing the actual data.
  • i.e. The colour scheme (e.g. iron, rainbow, or grayscale) that shows hot and cold areas in different shades.
  • Note: Choosing the right palette improves clarity for analysis and reporting; e.g., “Rainbow” for highlighting subtle electrical faults.
116. Passive Infrared System
  • Definition: A thermal imaging system that does not emit its own energy source but instead detects the natural infrared radiation emitted by objects in its field of view.
  • i.e. The standard type of thermal camera used in inspections.
  • Note: Most thermography cameras for M&E inspections are passive systems. Active systems are when extra heating or cooling is needed to reveal faults (e.g. in building materials).
117. Peak-Hold
  • Definition: A feature in thermal instruments that locks and displays the highest recorded temperature reading for a set period of time.
  • i.e. A function that “freezes” the hottest spot detected so it’s easy to review.
  • Note: Useful in thermography when scanning moving targets or fluctuating loads, ensuring the maximum temperature is not missed.
118. Photon-Detector
  • Definition: A type of infrared detector that directly senses photons, offering very fast response times (microseconds) and high sensitivity, but usually requires cooling and has a limited spectral response.
  • i.e. A high-speed sensor used in advanced infrared cameras for detecting rapid temperature changes.
  • Note: Commonly found in cooled MWIR cameras for research, aerospace, or high-temperature industrial applications where fast response is critical.
119. Photoconductor
  • Definition: A radiation-sensitive resistor whose electrical resistance decreases when exposed to infrared radiation.
  • i.e. A special material that becomes more conductive when it absorbs heat energy.
  • Note: Used in some infrared detectors, though less common today compared to microbolometers or photon detectors.
120. Photon
  • Definition: The smallest unit (quantum) of electromagnetic energy. In physics terms, its energy is defined as E = hf and momentum as hf/c (where h is Planck’s constant, f is frequency, and c is the speed of light).
  • i.e. A tiny “packet” of light or infrared energy.
  • Note: Infrared cameras detect streams of photons emitted by objects to create thermal images.
121. Photovoltaic Detector
  • Definition: An infrared detector that generates an electrical current directly when exposed to radiant energy.
  • i.e. A sensor that turns incoming heat energy into electricity without needing an external power source.
  • Note: Used in some cooled infrared systems for high-speed, sensitive measurements, especially in scientific and aerospace thermography.
122. Pixel
  • Definition: The smallest picture element in a digital image; each pixel represents one measurement point in a thermal image.
  • i.e. A single “dot” in the thermal picture that shows the temperature at that spot.
  • Note: More pixels (e.g. 640×480 vs 160×120) mean higher resolution and greater detail in thermography.
123. Planck, Max Karl Ernst Ludwig
  • Definition: A German physicist who introduced quantum theory into the blackbody radiation equation, leading to the formulation of the blackbody curves.
  • i.e. The scientist who explained how objects give off heat radiation at different temperatures.
  • Note: Planck’s law forms the basis of infrared thermography, as it defines how all objects emit infrared radiation depending on temperature.
124. Planck’s Law (Radiation Theory)
  • Definition: The equation that governs the spectral distribution of blackbody radiation, describing how objects emit electromagnetic energy at different wavelengths depending on temperature.
  • i.e. The math that explains how hot objects give off heat and light.
  • Note: Shows that hotter objects emit more radiation and at shorter wavelengths.
125. Polymeric Material
  • Definition: A class of synthetic materials made from long-chain polymers, engineered for use in infrared (IR) inspection windows as an alternative to crystal optics. These materials are designed to transmit infrared energy while providing mechanical strength and electrical safety.
  • i.e. A durable plastic-like material used in IR windows that allows thermographers to scan electrical equipment safely without opening panels.
  • Note: Polymeric IR window materials typically offer higher impact strength and arc resistance compared to crystal windows.
126. Post-Inspection Process
  • Definition: The final workflow that covers infrared report submission, issue verification, follow-up rectifications, and formal conclusion of the inspection.
  • i.e. A follow-up stage after the inspections are completed, where findings are reviewed, faults are fixed and confirmation scans are done before closing the job.
  • Note: Conducted both off-site and on-site to ensure all findings are properly addressed.
127. Pre-Inspection Process
  • Definition: A structured preparation phase carried out before the actual thermal inspection to plan scope, confirm documentation, assign qualified personnel, and verify all instruments and safety requirements.
  • i.e. Essential planning stage before actual site inspection, coordinated between thermographers and facility personnel.
  • Note: To be done at least 1 week before actual inspection.
128. Principal Plane
  • Definition: A reference plane in optics that simplifies how complex lens systems are modeled, treated as if they were a single thin lens at the effective focal length.
  • i.e. The imaginary flat line inside the lens where light is bent as if all the focusing happens there.
  • Note: Mainly relevant for advanced lens design and calibration; not typically adjusted in routine thermography but important in precision optics.

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129. Qualified Thermographer
  • Definition: A certified thermographer who also possesses relevant subject matter expertise (e.g. M&E, Building etc).
    • i.e. A thermographer officially trained to perform advanced thermography tasks.
      • An infrared thermographer who is trained and qualified to perform advanced thermographic inspections and formally validate inspection reports.
    • Note: Under Singapore Standards, a Qualified Thermographer is required to be at least Level-2 Certified.
130. Qualitative Measurement
  • Definition: A thermography method focused on interpreting thermal images based on contrast to identify anomalies, without assigning exact temperature values.
  • i.e. Looking for “hot” or “cold” patterns, not exact numbers.
    Note: Commonly used for quick scans and fault detection; best suited for screening or comparative analysis rather than precise diagnostics.
131. Quantitative Measurement
  • Definition: A thermography method that captures thermal images with accurate temperature values, used to determine whether a target meets specified criteria or thresholds.
  • i.e. Measuring the exact temperature, not just spotting patterns.
  • Note: Essential for compliance reporting, where precise temperature data is required.
132. Qualitative Analysis
  • Definition: An analysis method focused on identifying structural, material, or relative conditions without requiring exact temperature values.
  • i.e. Spotting heat patterns and differences instead of measuring exact numbers.
  • Note: Commonly used for fast scans or large-area inspections where relative contrasts are more important than precise data.
133. Quantitative Analysis 
  • Definition: An analysis method focused on assigning numerical temperature values or radiant energy levels to objects or processes for precise evaluation.
  • i.e. Measuring exact heat values instead of just spotting patterns.
  • Note: Essential for diagnostics and compliance reporting, requiring proper corrections (e.g. emissivity, distance, reflected temperature).

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134. Radian
  • Definition: A unit of angular measurement, defined as the angle created when the arc length equals the radius of a circle.
  • i.e. One radian = 57.3 degrees.
  • Note: Useful in thermography optics, as lens angles (like IFOV or FOV) are often expressed in milliradians.
135. Radiance
  • Definition: The total intensity of infrared energy (radiant flux) emitted from a surface per unit area, per unit angle, and per unit time (W/m2/sr). It includes emitted, reflected, and transmitted radiation.
  • i.e. The heat energy leaving a surface that the camera “sees.”
  • Note: Radiance is the actual signal detected by an infrared camera, forming the basis for temperature measurement.
136. Radiant Power
  • Definition: The total infrared energy emitted from an object per unit of time, measured in watts (W).
  • i.e. The total heat energy an object gives off every second
  • Note: In thermography, radiant power is the source of what the infrared camera detects before it is scaled into radiance or temperature.
137. Radiation
  • Definition: Heat transfer through electromagnetic waves, where energy moves directly from a warmer object to a cooler one without needing a medium (can travel through a vacuum).
  • i.e. Heat that travels in waves, like sunlight warming your skin.
  • Note: In thermography, radiation is the principle that makes imaging possible, as infrared energy travels from the target to the detector.
138. Radiator
  • Definition: A device that emits infrared radiation as heat, typically by transferring thermal energy from hot fluid or surfaces to the surrounding air.
  • i.e. A heater that gives off warmth you can feel without touching.
  • Note: In thermography, radiators can appear as strong heat sources and should be accounted for when analysing surrounding thermal patterns.
139. Radiometer
  • Definition: An instrument that measures the intensity of radiation, calibrated either in terms of power (watts) or equivalent temperature.
  • i.e. A device that tells how strong the heat energy is.
  • Note: In thermography, radiometers are used for precise scientific measurements rather than everyday maintenance inspections.
140. Radiometric Calibration
  • Definition: A controlled adjustment carried out in a laboratory or factory where an infrared camera is aligned against precision blackbody sources to ensure accurate and traceable temperature measurements.
  • I.e. Verifying that an infrared camera’s thermal readings correspond correctly to actual target temperatures during inspections.
  • Note (Pro-Tip) Without regular calibration, temperature drift may lead to overlooked hot spots, incorrect fault severity assessment, or unreliable inspection reports.
141. Range
  • Definition: A camera specification indicating the span of temperatures measurable, set by two blackbody calibration points.
  • i.e. The window where a thermal camera records valid readings.
  • Note: Ensure the selected infrared camera has the proper range for the target application.
142. Rankine 
  • Definition: A temperature scale based on 0 °R equals to absolute zero temperature, and uses the same degree interval as the Fahrenheit scale, meaning a 1°R change is equals to a 1°F change.
  • i.e. Rankine begins at the coldest point possible and rises like Fahrenheit.
  • Note: Commonly used in U.S. based engineering and thermodynamic formulas where Fahrenheit units are the standard.
143. Reference Temperature
  • Definition: A baseline temperature used as a comparison point for measured values
  • i.e. A fixed temperature chosen to judge if a thermal reading is higher or lower.
  • Note: Ensure a proper reference temperature is established to standardise inspection results and fault evaluation.
144. Reflection
  • Definition: The fraction of infrared radiation reflected by a surface compared to the radiation it receives, expressed as a value between 0 and 1.
  • i.e. How much infrared energy bounces off a surface instead of being absorbed.
  • Note: Ensure reflection is considered when inspecting shiny, metallic, or polished surfaces, as it can affect accurate temperature measurement.
145. Reflectivity Corrections
  • Definition: Adjustment applied to prevent the influence of reflected infrared so the measured surface temperature represents true emission.
  • i.e. Removing mirror heat.
    Note: Angle thermal camera 10 – 30° off axis to avoid glare, or use high-emissivity tape patch (≈0.95) on shiny spot and measure on the patch.
146. Reflectance (ρ)
  • Definition: A material property describing how much infrared radiation is reflected, influenced by surface condition, temperature, and material type.
  • i.e. The measure of a surface’s ability to bounce back infrared energy.
  • Note: Ensure reflectance is considered when inspecting shiny, metallic, or polished surfaces, as it can affect accurate temperature measurement.
147. RAT (Reflected Apparent Temperature)
  • Definition: A compensation value representing the infrared radiation reflected from surrounding objects onto the measured surface, important for low-emissivity or reflective materials.
  • i.e. Heat seen on a surface that comes from other sources.
  • Note: Ensure RAT is measured or estimated correctly to avoid errors when inspecting shiny, metallic, or polished surfaces.
148. ROI (Region of Interest)
  • Definition: A specific area in a thermal image selected for focused analysis of temperature data.
  • i.e. A marked zone where minimum, maximum, and average temperatures are calculated.
    Note: Ensure ROI is applied within reporting software to isolate critical areas for accurate analysis.
149. Relative Humidity (% RH)
  • Definition: The percentage of water vapor present in the air, compared to the maximum it can hold at the same temperature and pressure.
  • i.e. How full the air is with moisture.
  • Note: High RH can cause condensation on cold surfaces and affect infrared readings.
150. RTC (Reflected Temperature Compensation)
  • Definition: A camera or software setting that corrects the influence of reflected infrared radiation on measured temperatures, especially for low-emissivity surfaces.
  • i.e. A compensation step that removes background heat reflections from shiny objects.
    Note: When inspecting low-emissivity materials, apply RTC by inputting reflected temperature into the camera or software (often close to ambient temperature when indoors).
151. Repeatability
  • Definition: The ability of an instrument to consistently reproduce the same measurement under the same conditions, within a small margin of error.
  • i.e. How reliably a thermal camera gives the same reading when measuring the same spot again.
    Note: Ensure repeatability is verified during calibration to confirm instrument stability.
152. Remote Sensing
  • Definition: The process of obtaining measurements from a distance without direct contact between the instrument and the target object.
  • i.e. Measuring heat patterns on equipment using a thermal camera without touching it.
    Note: Essential when physical access is unsafe or impractical, e.g. high-voltage systems or moving machinery.
153. Rescan
  • Definition: A follow-up infrared inspection conducted after corrective actions has been carried out.
  • i.e. A scheduled 2nd inspection to confirm that the anomaly has been resolved.
  • Note: Rescans should be conducted when the system is back under normal load to verify true operating temperature.
154. Resolution
  • Definition: The ability of a thermal imaging system to distinguish fine details, measured as the smallest resolvable angle or pixel density within the Field Of View.
  • i.e. How clearly a thermal camera shows details in an image.
  • Note: Higher resolution is needed for small targets or distant measurements.
155. Responsivity
  • Definition: A measure of detector performance, showing how much the detector’s output changes in response to a difference in incoming thermal power.
  • i.e. How strongly a thermal detector reacts when more or less infrared energy hits it.
  • Note: This is a detector specification, not a camera specification. Higher detector responsivity improves overall thermal sensitivity.
156. Roof Moisture Survey
  • Definition: A building inspection application for detecting trapped moisture in roofing systems by measuring thermal inertia differences between dry and wet insulation.
  • i.e. Using infrared imaging to spot hidden wet areas beneath a roof surface.
  • Note: Ensure surveys are performed under proper heating/cooling conditions to highlight thermal contrasts.

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157. Saturation Colour
  • Definition: A display setting where pixels outside the selected level/span are shown in overflow (above range) or underflow (below range) colours. A third red saturation colour indicates detector overload.
  • i.e. Colours on a thermal image that flag values beyond the set viewing range.
  • Note: If red detector saturation appears, change temperature range to ensure accurate data.
158. Scale Sensitivity
  • Definition: The minimum temperature step that can be set in the system’s intensity scale, often finer than the detector’s own sensitivity (NETD).
  • i.e. The smallest adjustment size for temperature display on a thermal image.
  • Note: Ensure scale sensitivity is set appropriately, finer steps (e.g. 0.1 °C) allow for offline image improvement (e.g. noise reduction).
159. Selective Radiator
  • Definition: A thermal source that emits radiation strongly in specific wavelength bands while emitting little or none in others.
  • i.e. A radiator (e.g. flames) that gives off heat energy only in certain parts of the spectrum.
  • Note: In thermography, ensure selective radiators are recognised since their uneven radiation can affect temperature readings.
160. Sensitivity
  • Definition: The smallest temperature difference a thermal camera can detect, typically specified as NETD (Noise Equivalent Temperature Difference).
  • i.e. The ability of a thermal camera to see very small changes in surface temperature.
  • Note: Ensure sensitivity (NETD) is considered when selecting a camera. Lower NETD value means higher sensitivity and clearer detection of subtle thermal anomalies.
161. Sensor
  • Definition: The component that detects infrared radiation and converts it into electrical signals; sometimes used to refer to the detector.
  • i.e. The part of a thermal camera that turns heat energy into data.
  • Note: Ensure sensor type (e.g. cooled vs. uncooled) is considered when selecting a camera, as it directly impacts image quality, sensitivity, and application suitability.
162. Severity Criteria
  • Definition: A guideline or standard used to rank thermal anomalies by their urgency and repair priority.
  • i.e. A way to decide which thermal faults need repair first.
  • Note: Severity criteria should be based on the target material or component’s temperature tolerance, since damage thresholds vary by design and rating.
163. Solar Loading
  • Definition: Temperature rise caused by recent sunlight exposure.
  • i.e. Essential for thermal inspections on Solar Photovoltaic (PV) Systems.
  • Note: Irradiance ≥ 600 W/m² is recommended for reliable results.
164. Span
  • Definition: A user-controlled camera display setting that defines the interval of temperatures shown on the thermal image.
  • i.e. The width of the temperature range visible on the camera screen.
  • Note: Narrow span increases contrast for subtle anomalies. Wide span displays a broader temperature range with less detail.
165. Spatial Resolution
  • Definition: The smallest object size a thermal camera can resolve at a given distance, determined by detector pixel size and optics, expressed as IFOV (mrad).
  • i.e. How small a target can be while still appearing clearly in the thermal image.
  • Note: Ensure spatial resolution is matched to the inspection distance — finer resolution is needed for small or distant components to avoid missed anomalies.
  • When selecting a camera, ensure spatial resolution is considered. Lower mrad values (e.g. 0.65 mrad) allows clear detection of small or distant components, while higher mrad values (e.g. 3.3 mrad) may blur small faults into the background.
166. Specific Heat
  • Definition: A material property that indicates the amount of thermal energy (joules) required to raise the temperature of one gram of a substance by 1 °C.
  • i.e. How much heat a material must absorb to get warmer.
    Note: Materials with different specific heat warm up and cool down differently, affecting how thermal patterns appear during inspections (e.g. Metals, with low specific heat, heat up and cool quickly, so heat appears and disappears faster in thermal images.)
167. Spectral
  • Definition: The wavelength range of the electromagnetic spectrum to which a thermal camera is sensitive, also called spectral range or spectral response.
  • i.e. The infrared “band” a camera can see, e.g. 3–5 µm (MWIR) or 8–14 µm (LWIR).
  • Note: Ensure spectral range matches the application. LWIR (Long-Wave Infrared) is common for M&E and building inspections.
168. Spectral Absorption
  • Definition: The property of a filter or gas that allows certain wavelengths of radiation to pass through while absorbing others.
  • i.e. In air, gases like water vapor and CO₂ absorb parts of the infrared spectrum, reducing how much energy reaches the camera.
  • Note: Minimise long-distance measurements, as air and gases may weaken infrared signals.
169. Spectral Radiant Emittance (Mλ)
  • Definition: The amount of radiant energy an object emits per unit time, per unit surface area, and per unit wavelength.
  • i.e. How much infrared energy a surface gives off at each wavelength.
  • Note: During thermal inspections, correction is often done by setting emissivity to 0.95 for most materials. Pay attention to low-emissivity surfaces (e.g. shiny or reflective metals), where emissivity tape, paint, or material-specific settings are required for accurate results.
170.Spectral Emission
  • Definition: Radiation from a source that is concentrated in specific wavelength bands, with little or no emission in other parts of the spectrum.
  • i.e. Heat energy given off only at certain infrared bands.
  • Note: In thermography, ensure spectral emission is recognised since emitters like flames produce uneven radiation, which can affect temperature readings.
171. Specular
  • Definition: A surface characteristic where radiation is reflected in a mirror-like manner, typical of shiny or polished materials.
  • i.e. A shiny surface that bounces heat.
  • Note: During inspections, adjust angle or use emissivity tape/paint to overcome reflections caused by specular surfaces.
172. Spot Meter (Camera Feature)
  • Definition: An instrument that converts infrared radiation from a single spot on a surface into a temperature reading, guided by a laser pointer for aiming.
  • i.e. Also known as a spot thermometer (or handheld IR thermometer).
  • Note: Commonly used for quick spot checks, providing only a single-point temperature reading without imaging.
173. Spot Size
  • Definition: The smallest object size that can be accurately resolved and measured at a given distance by a thermal camera’s optics.
  • i.e. The minimum size a target must be for a correct temperature reading.
  • Note: In thermography, ensure the spot size is smaller than the object being measured. As a rule, the target should cover at least a 3×3 pixel area for reliable results.
174. Spot Size Ratio
  • Definition: A camera specification, typically listed on handheld spot thermometers, that expresses the ratio of the measurement distance (D) to the diameter of the spot size (S) the device can resolve.
  • i.e. The maximum distance at which a small target can still be measured accurately.
  • Note: Higher D:S ratio allows accurate measurements at greater distances (e.g. 120:1 ratio can measure a 1 cm target from 120 cm away).
175. SNF (Slit Response Function)
  • Definition: A detector performance specification that describes how the system responds to a narrow slit of radiation, used to evaluate the spatial resolution and sharpness of the infrared detector.
  • i.e. A way of checking how clearly a detector can “see” fine details in a thermal image.
  • Note: Routine inspection infrared cameras (uncooled) have lower SRF around 40–60%, research cameras (cooled) achieve higher SRF around 80%.
176. Stability
  • Definition: A system specification that measures how consistently a thermal imager maintains accuracy over time, showing how little a reading drifts from its original value.
  • i.e. How steady a temperature reading stays without shifting.
  • Note: In inspection cameras, higher stability ensures reliable long-term measurements. E.g. A stable camera may drift < ±2 °C over 8 hours, while a less stable system might drift by > ±5 °C.
177. Standards
  • Definition: Industry-recognised guidelines or references that establish the fundamental rules for conducting thermal inspections and reporting, ensuring consistency, accuracy, and comparability across the field.
  • i.e. The main reference documents that thermographers follow to keep practices uniform.
  • Note: E.g. ISO 18436-7, ASNT SNT-TC-1A, NFPA 70B, SS TR119 which define training, certification, and inspection methods for thermography.
178. Steady-State Condition
  • Definition: A thermal behavior where an object’s temperature has stabilised and no longer changes significantly with time, also called thermal equilibrium.
  • i.e. When an object’s heat has stopped rising or falling.
  • Note: Ensure steady-state is reached before measuring thermography readings. Unstable conditions may cause misleading temperature data.
179. SWIR (Short-Wavelength Infrared)
  • Definition: A portion of the infrared spectrum ranging from approximately 1.4 to 3.0 micrometers (µm).
  • i.e. Heat waves just beyond NIR, not typically used for thermal imaging.
  • Note: SWIR is mainly applied in imaging through smoke or haze, and night vision surveillance but not commonly used in maintenance thermography.

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180. Temperature
  • Definition: A thermal state variable that expresses the amount of energy contained in a body, representing its thermal energy density.
  • i.e. How hot or cold an object is.
  • Note: In thermography, ensure temperature readings are interpreted with emissivity, reflection, and environmental factors in mind, as apparent temperature may differ from true surface temperature.
181. Temperature Range
  • Definition: The overall span of temperatures an infrared camera can measure, defined by calibration limits between two blackbody reference points. Cameras may have multiple selectable ranges.
  • i.e. The minimum to maximum temperatures a thermal camera can measure and display.
  • Note: Ensure the specified range is understood correctly, as it may refer to the displayed measurement range or the camera’s own operating range.
182. Temperature Scale
  • Definition: A display setting that maps image colors or grayscale to two limiting temperature values, defining how the infrared image is shown.
  • i.e. The color range on the screen between the lowest and highest displayed temperatures.
    Note: On most infrared cameras, the temperature scale is adjusted through the Level/Span controls (sometimes called manual mode). Auto-adjust mode sets it automatically, but manual fine-tuning typically reveals faults more clearly. Too wide a scale may hide details, while a narrow scale enhances contrast for subtle anomalies.
183. Thermal Bridging
  • Definition: Localised heat transfer through a part of a building envelope that has lower thermal resistance than the surrounding construction, creating a preferential path for heat flow.
  • i.e. Heat takes an easier path through materials such as structural members, junctions, or areas with reduced or interrupted insulation.
  • Note: Thermal bridges can produce characteristic hot or cold surface patterns in a thermogram, depending on the direction of heat flow and whether the surface is viewed from inside or outside. Their appearance should be interpreted together with building construction, indoor/outdoor temperature conditions, and other environmental factors.
184. Thermal Capacitance
  • Definition: A material property that describes the amount of heat energy a material can store, influencing how it responds to heating and cooling.
  • i.e. How much heat a material can hold.
  • Note: Materials with different thermal capacitance warm up and cool down differently, affecting how thermal patterns appear during inspections (e.g. Metals, with low thermal capacitance, heat up and cool quickly, so heat appears and disappears faster in thermal images.)
185. Thermal Conductivity
  • Definition: A material property that measures how easily heat is conducted through a substance, expressed in W/m·K (watts per metre-kelvin).
  • i.e. How easily heat moves through a material.
  • Note: Metals have higher conductivity (e.g. copper busbars), transfering heat faster. Insulation materials (e.g. PVC cables) have lower conductivity, transfering heat slower.
186. Thermal Gradient
  • Definition: The rate of temperature change across a distance, often displayed as a line graph (thermal profile) in thermal imaging software.
  • i.e. A line showing how temperature rises or falls from one point to another.
  • Note: Typically viewed in reporting softwares, steeper gradients generally indicate faults or poor contact.
187. Thermal Radiation
  • Definition: Electromagnetic energy emitted by matter due to its temperature, with wavelengths typically between 0.7 µm and 100 µm in the infrared region.
  • i.e. Heat energy given off as invisible infrared waves.
  • Note: Infrared cameras detect only emitted infrared radiation, which is why temperature measurement is non-contact.
188. Thermal Image / THERMOGRAM
  • Definition: An infrared image produced by a thermal imager that displays surface temperature distributions, with different colors or grayscale tones representing different temperature values.
  • i.e. The recorded evidence used for analysis and reporting, also known as a thermogram.
  • Note: Accurate interpretation depends on proper calibration, emissivity settings, and environmental considerations. Apply the Four-T Framework (Temperature, Tool, Target, Technique) for reliable inspections.
189. Thermal Tuning
  • Definition: The adjustment of a thermogram’s displayed temperature interval, typically using level and span, to concentrate the available colors or grayscale tones over the temperature range of interest and improve thermal contrast.
  • i.e. Optimising the temperature scale so relevant thermal patterns, gradients, and anomalies are easier to recognise and interpret.
  • Note: Thermal tuning changes how the thermal data is displayed, not the underlying temperature measurements. A narrower span generally increases visual contrast, while a wider span reduces contrast and may make subtle temperature differences harder to see.
190. Thermography
  • Definition: An imaging procedure that uses infrared measurement technology to visualize thermal radiation and display the surface temperature distribution of objects with a thermal imager.
  • i.e. A method of taking pictures of heat to see how hot or cold surfaces are.
  • Note: Widely applied in M&E, building inspections, and industrial maintenance to detect faults before failure.
191. Thermometer
  • Definition: An instrument used to measure temperature, typically through direct contact or air sensing.
  • i.e. A tool that tells how hot or cold something is.
  • Note: Thermometers / spot thermometers provide a single-point reading, often used for quick checks.
192. Transmissivity (T)
  • Definition: A radiative property describing the fraction of infrared energy that passes through a material, expressed as a value between 0 and 1.
  • i.e. How much heat radiation goes through a material.
  • Note: When inspecting infrared-transparent materials (e.g. inspection windows, filters), accurate readings require considering the Reference Formula: A.R.T. = 1. If an object’s Transmissivity is high, its Absorptivity and Reflectivity are low.
193. Transmittance
  • Definition: A material property that measures the ability of a material to pass infrared radiation without absorbing or reflecting it, expressed as the ratio of transmitted radiant energy to total incident energy.
  • i.e. How much infrared energy passes through a material.
  • Note: When using infrared windows or protective filters, input the correct τ (e.g. 0.85 or 85%) into the camera for accurate results.

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194. Uncooled Thermal Cameras
  • Definition: Thermal cameras that use uncooled infrared detectors (typically microbolometers) operating near room temperature, without cryogenic cooling.
  • i.e. Standard thermal cameras that detect heat without special cooling systems.
  • Note: Most common for M&E and building inspections.

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195. Viewfinder
  • Definition: A small built-in display on a thermal camera that reproduces the final system image at reduced size and resolution, viewed by placing the eye directly against it.
  • i.e. A mini screen to look through, helping the operator frame and focus thermal images effectively.
  • Note: Useful in bright outdoor conditions where LCD screens are hard to see.
196. View Factor (Configuration Factor)
  • Definition: In radiative transfer, the ratio of thermal radiation leaving one surface (A) that directly strikes another surface (B).
  • i.e. How much one object “sees” another in terms of heat exchange.
  • Note: Applied in thermal engineering and energy modeling (e.g. furnace design, radiation heat transfer analysis, simulations), and less relevant in routine thermography inspections.

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197. Wavelength
  • Definition: The distance between two consecutive peaks (or cycles) of a wave, typically measured in micrometers (µm) for infrared radiation.
  • i.e. The length of one “wave” in light or heat energy.
  • Note: Different cameras are designed for specific infrared wavelengths. E.g. LWIR (8–14 µm) for general maintenance inspections, MWIR (3–5 µm) for high-temperature targets.
198. Wavelength Dependence (Spectral Behavior)
  • Definition: The variation of radiative properties (emissivity, reflectivity, transmissivity), depending on the infrared wavelength.
  • i.e. Heat behaves differently at different infrared wavelengths.
  • Note: Most M&E and building inspections fall within the LWIR wavelength (Long-Wave Infrared).
199. Window Correction
  • Definition: A camera compensation feature that applies material-specific transmittance (τ) and temperature adjustments to correct measurement errors when imaging through an IR-transparent window.
  • i.e. A setting that fixes temperature readings when shooting through an infrared window.
  • Note: When using infrared windows or protective filters, input the correct τ (e.g. 0.85 or 85%) into the camera for accurate results.

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200. Zoom Lens Effects
  • Definition: Optical performance changes caused by using a zoom lens on a thermal camera, which alters the Field Of View (FOV), Instantaneous Field Of View (IFOV), and spot size.
  • i.e. Zooming in changes how much detail and area the camera captures.
  • Note: Zoom lenses should be factory calibrated and verified annually to ensure accurate temperature readings.

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