Detecting Infrared Waves, Not Visible Light
The first thing to know about these cameras is they don’t work like regular cameras. Regular daylight cameras and the human eye both work on the same basic principle: visible light energy hits something, bounces off it, a detector receives the reflected light, and then turns it into an image.
Thermal imagers make pictures from heat, not visible light. Heat (also called infrared or thermal energy) and light are both parts of the electromagnetic spectrum, but a camera that can detect visible light won’t see thermal energy, and vice versa. Thermal cameras capture infrared energy and use the data to create images through digital or analog video outputs.