const int LDR_PIN = A0; 
const int LED_PIN = 9; 

void setup() {
    pinMode(LED_PIN, OUTPUT);
    digitalWrite(LED_PIN, LOW); 
}

void loop() {
    int lightValue = analogRead(LDR_PIN);
    if (lightValue < 500) { 
        digitalWrite(LED_PIN, HIGH); 
    } else {
        digitalWrite(LED_PIN, LOW); 
    }
}