int pinLDR = 15;
int led1 = 21;


void setup() {
  Serial.begin(9600);
  pinMode(pinLDR, INPUT);
}

void loop() {
  int lux = analogRead(pinLDR);
  if (lux >= 1500) {
    analogWrite(led1, HIGH);
  } else {
    analogWrite(led1, LOW);
  }

  delay(200);
}