// Interfacing Arduino uno with LDR sensor 
const int ledPin = 13; // digital pin 5  
const int ldrPin = A0; // analog pin 0 
void setup() {  
Serial.begin(9600); 
pinMode(ledPin, OUTPUT); // Here LED is determined as an output or an indicator. 
pinMode(ldrPin, INPUT); // Here LDR sensor is determined as input. 
} 
void loop() { // Void loop is ran again and again and contains main code. 
int ldrStatus = analogRead(ldrPin); 
if (ldrStatus >= 400) {digitalWrite(ledPin, HIGH); // If LDR senses darkness led pin high
                                                  // that means led will glow.
Serial.print("Darkness over here,turn on the LED :"); 
Serial.println(ldrStatus); 
} else { 
digitalWrite(ledPin, LOW); // If LDR senses light led pin low that means led will stop glowing. 
Serial.print("There is sufficient light , turn off the LED : "); 
Serial.println(ldrStatus); 
} 
}