int ldrPin = A0;   
int ledPin = 9;     
int ldrValue = 0;   
int ledBrightness = 0; 

void setup() {
  pinMode(ledPin, OUTPUT); 
}

void loop() {
  ldrValue = analogRead(ldrPin);
  ledBrightness = map(ldrValue, 0, 1023, 0, 255);
  
  analogWrite(ledPin, ledBrightness);

  delay(100);
}