int ldr = A0;
int x;
int led = 2;

void setup() 
{
  Serial.begin(9600);
  pinMode(led, OUTPUT);
}

void loop()
{
  x = analogRead(ldr);
  Serial.println(x); 

  if(x > 500) 
  {
    digitalWrite(led, HIGH);
  }
  else
  {
    digitalWrite(led, LOW);
  }
}