- An LDR or light dependent resistor is also known as photo resistor, photocell, photoconductor. It is a one type of resistor whose resistance varies depending on the amount of light falling on its surface. When the light falls on the resistor, then the resistance changes.
- These resistors are often used in many circuits where it is required to sense the presence of light. These resistors have a variety of functions and resistance.
- For instance, when the LDR is in darkness, then it can be used to turn ON a light or to turn OFF a light when it is in the light. A typical light dependent resistor has a resistance in the darkness of 1MOhm, and in the brightness a resistance of a couple of KOhm
Working
- This resistor works on the principle of photo conductivity. It is nothing but, when the light falls on its surface, the material conductivity reduces and the electrons in the device’s valence band are excited to the conduction band.
- These photons in the incident light must have energy greater than the band gap of the semiconductor material. This makes the electrons to jump from the valence band to conduction.
- These devices depend on the light, when light falls on the LDR then the resistance decreases and increases in the dark. When a LDR is kept in the dark place, its resistance is high and, when the LDR is kept in the light its resistance will decrease.
