Photo Resistor

const int pResistor = A0; // Photoresistor at Arduino analog pin A0
const int ledPin=13;       // Led pin at Arduino pin 9

//Variables
int value; // Store value from photoresistor (0-1023)

void setup(){//run setup
 pinMode(ledPin, OUTPUT);  // Set lepPin - 9 pin as an output
 pinMode(pResistor, INPUT);// Set pResistor - A0 pin as an input (optional)
}

void loop(){ //begin loop
  value = analogRead(pResistor);
  
  //You can change value "25"
  if (value > 25){
    digitalWrite(ledPin, HIGH);  //Turn led on
  }
  else{
    digitalWrite(ledPin, LOW); //Turn led off
  }

  delay(500); //Small delay
}