String serialData = "";
boolean onSerialRead = false;

int led1 = 7, led2 = 8, led3 = 12;

void setup() {
    Serial.begin(9600);
    pinMode(led1, OUTPUT);
    pinMode(led2, OUTPUT);
    pinMode(led3, OUTPUT);
}

void loop() {
    if(onSerialRead) {
        processSerialData();
    }
}

void serialEvent() {
  while (Serial.available()) {
    char inChar = (char)Serial.read();
    if (inChar == '\n') {
          onSerialRead = true;
    } else {
          serialData += inChar;
    }
  }
}

void processSerialData() {
    if(serialData.equals("lon1")) {
        digitalWrite(led1, HIGH);
    }
    if(serialData.equals("lon2")) {
        digitalWrite(led2, HIGH);
    }
    if(serialData.equals("lon3")) {
        digitalWrite(led3, HIGH);
    }
    if(serialData.equals("loff1")) {
        digitalWrite(led1, LOW);
    }
    if(serialData.equals("loff2")) {
        digitalWrite(led2, LOW);
    }
    if(serialData.equals("loff3")) {
        digitalWrite(led3, LOW);
    }
    Serial.println(serialData);
    serialData = "";
    onSerialRead = false;
}