lead sulfide (PbS)
Lead sulfide (PbS) is a semiconductor material used in photoresistors. This semiconductor material has its spectral sensitivity to infrared light at wavelengths longer than 1,000 nm.
Therefore, lead sulfide is also used in infrared sensors. The sensitivity curve has a slowly increasing linear progression and starts at about 600 nm.
The resistance value of photoresistors using lead sulfide as the light-sensitive material falls with increasing light intensity. A changein luminous intensity of one power of ten is roughly countered by a change in resistance of one power of ten.