text: what prevents thermal cameras from detecting temperatures under -10c? is it related to the band-gap of the photo-detectors? thermal cameras work in the infrared not in uv.  there are cameras that can sense temperatures below -10 c.    however, these are expensive and require special lens material.  at such long wavelengths glass is no longer transparent.  materials like germanium (an opaque metal in visible light but transparent in far infrared) are used to make lenses.    the cameras also require cooling.  you can imagine that a warm camera trying to see -10c would just see itself.  the lens and the ccd array will glow and wipe out the image unless they are cooled to well below -10c.  the signal from the cold object is also very weak so the cameras electrical noise becomes a big issue requiring more sophisticated electronics.  these concerns make such cameras very expensive.