How a TI Works
All objects have a certain temperature and emit waves of energy called infrared radiation. Hot objects emit more energy than cold objects. A thermal imager translates these energy waves into a viewable image, which shows a “heat picture” of a scene. On the screen of a thermal imager set to white-hot, hotter objects show as white, cooler objects show as black, and objects in between these temperatures are displayed in shades of gray.
In some respects, the detector in the thermal imager is similar to the human eye. The thermal imager’s detector (called a "focal plane array", or FPA) and the eye are both receivers. They receive electromagnetic energy and convert it into an image for our brains to interpret. The eye receives wavelengths of energy called “visible light,” while the FPA receives wavelengths of heat energy called “infrared.”
The human eye and the TI do not “see” through most materials. Drywall, plaster, concrete, steel, wood, paneling, down comforters, doors, sofas and the like are not transparent to visible light or infrared. They “see” only what is on the surface: colors for the eye, temperature differences for the TI. However, due to the unique characteristics of IR, you can see through thick smoke.