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Infrared Definitions & Terms

Knowing the basic infrared definitions & terms will help you better understand the infrared spectrum & help you use your thermal camera effectively.  Listed here are a few of the key points to get you started on your path to gaining the most knowledge in thermography.

For a larger list of terms, please see our terminology page.  And as always, if you have any questions, feel free to contact us.

Infrared Defined

What is Infrared?

Infrared radiation is electromagnetic radiation whose wavelength is longer than that of visible light (400-700 nm), but shorter than that of terahertz radiation (100 µm – 1mm) and microwaves (~30,000 µm). Every object gives off thermal radiation, and this energy can be viewed with an infrared camera.

Infrared energy emitted by objects travels at the speed of light which is 186,000 miles per second. Or 300,000 km per second.

Infrared energy is a form of light and therefore it obeys all the same laws of visible light.

What is Infrared Imaging?

Infrared imaging is the collection, recording, and displaying of light from a scene; can be known as Infrared or IR, Thermal Imaging, FLIR (forward looking infrared), or Thermography. ‘Infrared’ refers to light with longer wavelengths than that of visual light, and shows the thermal patterns emitted from, or reflected off of a target; thus, it does not require visual light.

What is Infrared Radiation?

Radiation is energy that is radiated or transmitted in the form of waves or particles. Anything NOT at Absolute Zero (-273° C, -459° F) emits infrared radiation, including the sun, icebergs, humans, animals, furniture, etc.

All infrared cameras and thermometers detect radiant heat, also known as infrared radiation, that increases with molecular activity. As an object becomes warmer, it radiates more energy which an infrared camera can detect in order to create a thermal image or thermogram.

What is a Thermogram?

A thermogram is a thermal image made by an infrared camera showing temperature differences in varying colors based on the color palette chosen by a thermographer. It is ONLY a visual depiction of radiated heat, NOT temperature.

What is Infrared Thermography?

Infrared Thermography is the discipline concerned with the acquisition, storage and analysis of radiated energy using a thermal infrared imaging system. The resulting images do not show temperature; they only depict radiated energy.

Infrared Cameras Inc. uses a hue palette to assign colors to molecular activity and an algorithm to allow our IR cameras to “see” temperature.

What are the Benefits of Infrared Thermography?

  • Temperature calculations are non-contact
  • Process does not have to be shut down – must be running
  • Will not deface or destroy the product
  • Transient phenomena or moving objects can be studied
  • Fast response, milliseconds
  • Temperature calculations of irregular shaped objects
  • Pattern observation and evaluation
  • Collection of large amounts of thermal data
  • Measurement through hazardous atmospheres
  • Measurement through special IR windows
  • Data easily stored for post analysis and trending

Associated Terms

What is a Qualitative Infrared Camera?

Qualitative cameras do not measure temperature. They simply display temperature differences in a few different palettes including black and white. These infrared cameras or thermal imagers are generally used by law enforcement, home inspectors, or coast guard for a number of purposes.

The police use infrared cameras to identify criminal activity at night just like we’ve seen on COPS.

Home and building inspectors use these systems to look for moisture intrusion or energy loss in building envelopes.

And the coast guard or any other water bound vessel may use infrared for search and rescue or to see through certain weather conditions such as fog or rain.

Firefighters also use qualitative cameras to see through smoke and locate survivors in burning buildings.

Qualitative vs. Quantitative Infrared

What is a Quantitative Infrared Camera?

Quantitative cameras can measure temperature. These cameras are technically known as imaging radiometers.

Their purpose is to measure the radiant energy coming from a target to identify problem areas in electrical equipment, machinery, rotating equipment, kilns, boilers, and just about any kind of process that you can think of.

We also use quantitative cameras to monitor different types of processes or process equipment, and even the human body.

Qualitative vs. Quantitative Infrared

What is Temperature?

Temperature is a measurement of the average kinetic energy of the vibrating molecules that the temperature measurement device is relating to.

Temperature specifies the state of a body with respect to its ability to impart energy to other bodies.

What is Absolute Zero?

Theoretical temperature when molecules lose all vibrational kinetic energy. All objects above absolute zero ( -273° C or – 459° F) emit infrared energy.

What is Heat?

Heat is energy in transit from areas of higher molecular motion (higher temperature) to areas of lower molecular motion (lower temperature) independent of direction. When all of the molecules have the same kinetic energy we have a state called thermal equilibrium. There is no heat transfer in this state.

What are the Laws of Thermodynamics?

  • 1st Law
    • Energy must be conserved or exactly accounted for (it can be changed from one form to another form)
    • Heat that flows to an object must go somewhere, it cannot be created or destroyed
    • Energyin = Energyout + Energystored
  • 2nd Law
    • Heat always flows from a point of higher temperature to a point at lower temperature

What is Conduction?

Conduction is a point-by-point process of heat transfer. If one part of a body is heated by direct contact with a source of heat, the neighboring parts become heated successively. Thus if a metal rod is placed in a burner, heat travels along the rod by conduction. This may be explained by the kinetic theory of matter. The molecules of the rod increase their energy of motion. This violent motion is passed along the rod from molecule to molecule. In considering the flow of heat by conduction, it is sometimes helpful to compare the flow of heat to the flow of electricity. The temperature difference can be thought of as the pressure, or voltage, in an electrical circuit. The ability of a substance to transfer heat (its thermal conductivity) can be compared to electrical conductivity. When the temperature difference (or voltage) between two points is great, the driving force to move heat (or current) is high. The quantity of heat (or current) transferred will depend upon the temperature difference (or voltage difference) and the resistance to the flow of heat (or current) offered by the conductor.

What is Convection?

The method of heat transfer called convection depends upon the movement of the material which is heated. It applies to free-moving substances; that is, liquids and gases. The motion is a result of changes of density that accompany the heating process. Water in a tea kettle is heated by convection. A stove heats the air in a room by convection. When a liquid or gas is heated, its density (mass per unit volume) decreases; that is, it becomes lighter in weight. A warmer volume of gas will rise while a colder, and thus heavier, volume of gas will descend. This process is described as natural convection. A familiar example of natural convection is the circulation of air from a hot-air furnace. When a liquid or gas is moved from one place to another by some mechanical force, the process is known as forced convection. The circulation of air by an electric fan is an example of forced convection.

What is Emissivity?

The rate at which infrared energy is emitted by an object compared to that of a Blackbody at the same temperature and in the same wavelength.

What are Palettes?

Color palettes are convenient ways for you to see a thermal image. For instance, you may chose to have cold be the color blue, medium yellow and red hot. Or you might want everything black and white with everything over 80°F red. Or you might want cold to be purple and hot to be yellow.


Restrictions and Applications

What do infrared cameras see?

Infrared cameras only see the emitted or radiant energy from the 1st one thousandth of an inch of the surface of most solids and liquids.

Can infrared measure temperature?

  • Infrared cameras see heat in the form of radiant energy.
  • The thermographer measures the temperature of a target. You have to put the proper data into the camera in order to get accurate temperature measurements.
  • This means that setting up your camera before an inspection is important. It is also important to realize that you will be changing some of these settings in your camera during your inspection. (Of course this depends on the scope of equipment that you’re inspecting.)

Can you see through walls with an infrared camera?

Unlike the movies, with infrared, we cannot see through walls. We can only see temperature differences present due to the conduction, convection, or radiation of thermal energy. While shorter infrared waves can be seen as colors, as infrared waves get longer they give off radiation in the form of thermal energy. Infrared waves are considered to be energy. Infrared cameras look at radiated energy from the first 1/1000” of the surface.

What applications are infrared products used in?

Thermography, infrared building inspections, monitoring & control applications, medical imaging, communications, night vision, infrared photography, spectroscopy, military, research & development, process control, meteorology, astronomy, art history, biological systems, photobiomodulation, law enforcement, emergency services, military,, commercial, residential, and industrial.  Just to name a few… 😉

What are the industrial and commercial applications of infrared thermography?

This technique has many applications such as industrial electrical systems, furnaces, refractory, locating wet areas in large flat roofs, identifying heat loss in buildings, security and surveillance, and medical observations. Since you are looking at heat pictures, abnormal patterns often mean specific things: a high resistance electrical connection is hotter than other connections under the same conditions, missing insulation in a building wall will show up as a warm area on the exterior, a wet area on a flat compound roof is cooler than the area around it.

What are the benefits of a thermal building inspection?

Thermal building inspections are rapidly becoming the norm for business and residential constructions alike. Currently, buildings in the United States represent up to 71% of electrical consumption and generate over 39% of the nation’s carbon emissions. With the proper infrared tools and training, building inspectors can eliminate energy loss and help to prevent problems from escalating into costly repairs.

Infrared inspections can help reduce/eliminate:

  • High Energy Bills – often high utility bills can be traced to air leaks, inefficient windows, missing insulation, inefficient cooling/heating equipment, and/or poorly insulated ducts.
  • Mold & Mildew – High humidity and water damage can lead to mold and/or mildew resulting in wood rot, various structure damage, and health problems.
  • Dust – Poorly sealed duct work can result in high levels of dust.
  • Cold or Hot Rooms – differences in temperature from room to room can signify inadequate insulation, air leaks, and/or poor duct insulation.
  • Medical Costs – high indoor allergens, dust, mold, mildew, and pests can lead to health problems. Locating the sources of these occurrences can decrease health costs and can increase productivity.
  • Economy – Energy efficient buildings reduce our reliance on foreign natural gas and other fuels, while saving money and promoting local economic growth.

What are the differences between night vision and thermal imaging?

The main difference between night vision and thermal imaging is the ability to see in total darkness. Night vision utilizes existing light sources and amplifies them, while thermal imaging is actually reading the infrared radiation coming from an object, regardless of any visible light source, and a trained thermographer can utilize this information to get accurate temperature measurements.

What is camera resolution and why is it important?

At Infrared Cameras Inc, we offer a variety of resolutions with our cameras. The resolution of an infrared camera can be compared to a television or computer monitor resolution. The larger the resolution, the more pixels on the screen. The more pixels you have, the finer the detail of the image.