Have you noticed how the street lights automatically turn on at night? That is thanks to Photoresistors. A Photoresistor is resistor that changes its resistance depending on the illumination it receives. The higher the light intensity, the lower resistance it has. This property is called photoconductivity.

Theory of Operation 

    Photoconductivity: When light falls on a semiconductor, it frees more electrons than the semiconductor normally has. Those “free” electrons allow more current to follow, reducing the resistance of the semiconductor.

Technical Details

-    5VDC Analog

-    Datasheet:





  1) Connect the circuit as shown in the picture
  2) Upload this code to the Arduino
  3) Open the serial monitor and be sure the baud rate is set to 9600

void setup()
    Serial.begin(9600);  //Begin serial communication

void loop()
    //Reading Photoresistor and posting value on serial monitor

    //A short delay


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