The photo resistors are made from photo conductive semiconductor materials such as cadmium sulphide (CdS) and cadmium selenide (CdSe). The covalent bonds are broken when the light is incident on the semiconductor materials. Due to this electron-hole pairs are generated. Depends on the intensity of light incident on it the number of electron-hole pairs are generated.
The Light dependent resistor (LDR) is a type of variable non-linear resistor whose value of resistance depends on the value of light incident on it. The LDR is also known as photo resistor, photo conductors, photo conductive cells or simply photo cells. The LDR is a light controlled variable resistor. It is basically a resistor which has a resistance that varies depending upon the light intensity. The LDR is a highly resistive semiconductor that absorbs photons.
The resistance of LDR decreases with increasing incident light intensity.