Light Dependent Resistor (LDR) or Photoresistor

 Light Dependent Resistors (LDR) or Photoresistors are widely used in automatic street lights and garden lights. Ambient light falling on the device triggers an electronic circuit which switches off the lights. When light falls on the LDR, the resistance falls from a few mega ohms to a few hundred ohms. Lead sulphide and Indium antimonide are two important substances used in the manufacture of LDRs. LDR is a passive device and does not have a PN junction as in active devices like photodiodes and phototransistors. There is a lag between the change in illumination and change in resistance which makes LDR not suitable for fast switching purposes.




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