int ldr = A0;
int reading;
int threshold = 900;
int led = 3;

void setup()
{
  pinMode(ldr, INPUT);
  pinMode(led, OUTPUT);
  Serial.begin(9600);
  digitalWrite(led, HIGH);
  delay(500);
  digitalWrite(led, LOW);
}

void lightCheck(){
  reading = analogRead(ldr);
  Serial.print("reading = ");
  Serial.print(reading);
  if(reading >= threshold)
  {
    Serial.println(" daylight");
    digitalWrite(led, HIGH);
  }
  else{
    Serial.println(" nighttime");
    digitalWrite(led, LOW);
  }
  delay(1000);
}

void loop(){
  lightCheck();
}