Cadmium sulfide(CdS) is a semiconductor material used in photoresistors. This semiconductor material belongs to the II- VI compound semiconductors and has its highest sensitivity at a visible wavelength of 520 nm.
Cadmium selenide (CdSe), another semiconductor material for photoresistors, has its maximum sensitivity at 730 nm. The resistance value of these photoresistors drops with increasing light intensity. A change in light intensity of one power of ten is approximately countered by a change in resistance of one power of ten.