Sohail Ansari

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Light Dependent Resistor (LDR) & its Application

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It stands for Light Dependent Resistor or Photo-resistor, which is a passive electronic component, basically a resistor which has a resistance that varies depending of the light intensity. A photoresistor is made of a high resistance semiconductor that absorbs photons and based on the quantity and frequency of the absorbed photons the semiconductor material give bound electrons enough energy to jump into the conduction band. The resulting free electrons conduct electricity resulting in lowering resistance of the photoresistor. The number of electrons is dependent of the photons frequency.


Application :

As a switch : The most obvious application for an LDR is to automatically turn on a light at certain light level. For example


The circuit shown right shows a simple way of constructing a circuit that turns on when it goes dark.The increase in resistance of the LDR in relation to the other resistor which is fixed as the light intensity drops will cause the transistor to turn on.The value of the fixed resistor will depend on the LDR used, the transistor used and the supply voltage.

If we connect LED as a load then it will turn on in dark and turn off in presence of light. In this way we can use LDR in a various ways.If you have any other application then please reply below.

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