A Light Dependent Resistor (LDR) or a photo resistor is a non linear device whose resistivity is a function of the incident electromagnetic radiation.
- A light dependent resistor works on the principle of photo conductivity.
- Photo conductivity is an optical phenomenon in which the materials conductivity (Hence resistivity) reduces when light is absorbed by the material.
- When light falls then the resistance of the device has decreased.
- When a light dependent resistor is kept in dark, its resistance is very high. This resistance is called as dark resistance.
- It has high as 1012 ohm when LDR kept in dark.
- When light is incident on a photocell it usually takes about 8 to 12ms for the change in resistance to take place.
- While it takes seconds for the resistance to rise back again to its initial value after removal of light.
- Automatic street light system.
- ADC 0804.
- 8051 MicroController.