Our eyes are detectors, designed to detect visible light (or visible radiation). However, there are other forms of light that we cannot see. The human eye sees only a very small part of the electromagnetic spectrum – at one end of the spectrum we cannot see ultraviolet light, whilst at the other end our eyes cannot detect infrared. Infrared radiation lies between the visible and microwave portions of the electromagnetic spectrum, and the primary source of infrared radiation is heat or thermal radiation.

Any object with a temperature above absolute zero (-273.15°C or 0 Kelvin) emits radiation in the infrared region. Even objects we think of as being very cold, such as ice cubes, emit infrared radiation. We experience infrared radiation every day. The heat we feel from the sun, a fire or radiator, all are infrared and, although we cannot see it, the nerves in our skin feel it as heat. The warmer the object, the more infrared radiation it emits.

The Infrared Camera

Infrared energy (A) coming from an object is focused by the optics (B) onto an infrared detector (C). The detector sends the information to sensor electronics (D) for image processing. The electronics translate the data coming from the detector into an image (E) that can be viewed in the viewfinder or on a standard video monitor or LCD screen.

Infrared thermography is the art of transforming an infrared image into a radiometric one, which allows temperature values to be read from the image.