Lead compounds (PbS, PbSe and PbTe) are direct bandgap semiconductor materials whose application is confined to infrared detecting and thermal imaging. These semiconductors operate at wavelengths of 1-5.5 µm. They perform well at room temperature but can be cooled if better sensitivity is required. PbTe, PbSe and PbS detectors are widely used in flame detection, combustion control, non-contact temperature measurement, gas and moisture control, spectrophotometry, analytical and medical imaging.