In flash thermography, a brief pulse of light is used to heat the surface of a sample, while an infrared camera records changes in the surface temperature. As the sample cools, the surface temperature is affected by internal flaws such as disbonds, voids or inclusions, which obstruct the flow of heat into the sample.

Flash thermography, combined with TWI's Thermographic Signal Reconstruction (TSR) method provides the fastest, most quantifiable and repeatable approach to thermography for NDT. For many applications, TWI flash/TSR systems have proved to be viable, cost effective replacements for visual, ultrasound, radiography or laser shearography methods.