PbS and PbSe detectors are photoconductive sensors whose resistance decreases with increasing infrared light. PbS sensors operate from 1.3 µm to 3.2  µm with a peak sensitivity near 2.2 µm,  while PbSe sensors operate from 1.3 µm to 5.2  µm with a peak sensitivity near 4.2 µm. They can be used at room temperature or cooled with a thermoelectric cooler. Large active area devices (5mm x 5mm) are available. Both PbS and PbSe detectors are used in pyrometers for temperature measurements, as flame monitors, in gas sensors and in analytical instruments that utilise mid-infrared spectrophotometry (MIR).