int pins[] = {2, 3, 4, 5};

void setup() {
  for (int i = 0; i < 4; i++) {
    pinMode(pins[i], OUTPUT);
    digitalWrite(pins[i],HIGH);
  }
}

void loop() {
  for (int i = 0; i < 4; i++) {
        // briefky pulse the LED
    digitalWrite(pins[i], LOW);
    delay(1);                               // Change this delay to higher values (e.g. 100) to see the strobing effect in slow motion
    digitalWrite(pins[i], HIGH);
  }
}