LDR or Photoresistor Definition,Construction,Working

LDR

What is LDR?

LDR is a light dependent resistor its resistance is changes as the light falls on it.The resistance of a LDR decreases with increasing incident light intensity; In other words, it exhibits photo conductivity. LDR can be applied to light-sensitive detector circuits, and light-activated and dark-active switching circuits.LDR is also called as photoresistor.

Discovery

Idea of LDR or photo resistor is develop by Willoughby Smith in 1873.

Symbol of LDR

LDR Symbol

Construction

In LDR mainly four material are used which are given as cadmium sulphide (CdS),CdSe,PbS,TIS.In LDR two electrode are extended in inter digital pattern in order to increase contact area with the sensitive material.In this way ,it is possible to obtain a large ratio pf dark to light resistance.

An external power supply is necessary to generate a direction and provide path for the current to flow.

Working Principle of LDR

LDR is based on the principle that the resistance of semiconductor decrease when they are exposed to radiation.In other words such material have have high dark resistance and low irradiated resistance.So when radiation of sufficient energy falls on the LDR it causes the breakage of covalent bonds and generating the electron hole pair.

Advantages of LDR

1. High Sensitivity
2. Low cost
3. High Dark to light resistance ratio

Uses of LDR

1. For relay operation
2. As voltage regulator
3. In light sensor

Hope friends you under the concept of LDR or photoresistor please comment your views and share.