LIGHT DEPENDENT RESISTOR(LDR) | AUTOMATIC STREET LIGHT Control using LDR

Works on the principle of LDR:
In simple words , it works on principle of Photoconductivity
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When light falls i.e. when the photons fall on the device, the electrons in the valence band of the semiconductor material are excited to the conduction band. These photons in the incident light should have energy greater than the band gap of the semiconductor material to make the electrons jump from the valence band to the conduction band. Hence when light having enough energy is incident on the device more & more electrons are excited to the conduction band which results in large number of charge carriers. The result of this process is more and more current starts flowing and hence it is said that the resistance of the device has decreased. This is the most common working principle of LDR

Visualization of inverting action of BJT
   • Visualization of inverting action of BJT