int ledPin = 2;
int ldrPin = A0;
int lightintensity; // Ammount of light reaching to LDR

void setup()
{
Serial.begin(9600);

pinMode(ledPin, OUTPUT);
pinMode(ldrPin, INPUT);

}

void loop() {

lightintensity = analogRead(ldrPin);

if (lightintensity > 500) // When light intensity is beyond 500
{
digitalWrite(ledPin, HIGH);  // Then LED turns ON
Serial.print("Light intensity= ");
Serial.println(lightintensity);

}

else // When light intensity is not beyond 500
{
digitalWrite(ledPin, LOW);  // LED turns OFF
Serial.print("Light intensity= ");
Serial.println(lightintensity);

}

}