LDR + LED

const int LED = 9;

const int LDR = A0;

void setup() {

  pinMode(LED, OUTPUT);

}

void loop() {

  int a0 = analogRead(LDR);

  int light = max(map(a0, 0, 600, 1023, 0), 0);

  analogWrite(LED, light);

  delay(300);

}