LDR SENSOR: 

                                    LDR is a Light Dependent Resistor. It works on the photoconductivity principle. It is one type of resistor whose resistance varies depending on the amount of light falling on its surface. When the light falls on the resistor's surface then the resistance changes. These resistors are often used in many circuits where it is required to sense the presence of the light.We can interface LDR sensor with Arduino to detect the light.

Applications:

• It can be used in street lights.
• It can be used in mines areas.
• It can be used in hilly areas.
• By using laser, it can be used for safety purposes.

Sample Project Using Arduino:

     In this we are going to turn ON/OFF the LED whenever the LDR sensor senses the light.

Materials Required:

• ARDUINO UNO Board
• LDR
• Relay
• Bulb 
• Breadboard

Circuit Diagram:

Code:

int ldr = A0;  //initialize LDR is connected to pin in A0

int ldrvalue = 0;  //initialize value of LDR sensor is 0

int relay = 2;  // initialize relay is connected to pin 2

void setup()

{

pinMode(ldr,INPUT);  // Declare ldr as input

pinMode(relay,OUTPUT);  // Declare realty as output

Serial.begin(9600);  // Enabling serial monitor

}

void loop()

{

ldrvalue=analogRead(ldr);  // Read value of ldr, store it in ldrvalue

Serial.println(ldrvalue);  // print ldr value in serial monitor

if(ldrvalue<700)  // checking ldr value

{

  digitalWrite(relay,HIGH);   // if ldr value reaches specified value light can be turned on using relay

}

else

{

  digitalWrite(relay,LOW);  // if specified value exceeds then light is turned off using relay

  delay(200);

}

}

Serial Monitor Output: