Infrared Explained

What is thermal imaging, also known as infrared thermography?

Thermography is a name for a type of photography which is based on infrared wavelengths (as opposed to visible wavelengths). Conventional photography relies on reflected energy from a light source, be it the sun or artificial lighting, which is visible to our eyes. In contrast, thermal imaging relies on radiated energy in the infrared (IR) spectrum which is invisible to our eyes. All objects emit radiation energy within the IR spectrum and this IR radiation varies dependent on the temperature of that object.

If we could see this radiation, we could “see” the temperature of the surface of an object. As we cannot do this with our eyes, we need to use a device which can detect the “invisible” energy. A thermal imaging camera can do this. The camera builds a pixelated image of the IR radiation which allows us to “see” and measure the apparent temperature of the surface. Visualising the surface temperature helps the thermographer to decipher what is actually being detected, and then decide what can be inferred from this. Many times we know the environmental conditions around a building and so the surface temperatures give us information about insulation, thermal bridging and other building heat loss aspects.  But we can do much more than just this. As surfaces or objects which contain moisture behave differently to otherwise similar “dry” surfaces and objects, the presence of moisture can often be visualised by different thermographic techniques.

Thermography is non-invasive, non-contact and hence non-destructive. It can be used to scan large areas quickly and identify anomalies such as defective insulation or potential areas of dampness and trace and record paths in a way that other methods cannot.

When used in conjunction with other diagnostic tools and/or destructive testing, verification of the damp areas and migration paths can often be traced back to the source.

temp scale for explanation

Building thermography is often a qualitative methodology – that is to say we look at patterns and comparison rather than absolute temperatures. Therefore, thermal images are often used with the temperature scale removed as absolute temperatures are not important but anomalies, patterns and relative temperatures are. ScanTherm normally uses a high contrast “rainbow” scale or “palette”. The scale shows relatively cold (black/purple/blue) to relatively hot (yellow/red/white), but the values will vary from image to image. If absolute temperatures are required they will be indicated. An example thermal image is shown for reference to the right.