int t = 500;
void setup() {
  for(int led = 1; led <= 8; led++)
    pinMode(led, OUTPUT);
}

void loop() {
  for(int i = 1; i <= 8; i++){
    for(int j = 1; j <= i; j++){
      digitalWrite(i, HIGH);
      delay(t);
      digitalWrite(i, LOW);
      delay(t);
    }
  }
}