mid_11_ardu.ino

int light = 9;

void setup() {
  Serial.begin(9600);
  pinMode(light, OUTPUT);
}

void loop() {
  if(Serial.available()) {
    char ind = Serial.read();

    if(ind == 'H' || ind == 'h')
      digitalWrite(light, HIGH);
    if(ind == 'L' || ind == 'l')
      digitalWrite(light, LOW);
  }
}