int L = 8;
int vorher = 0;
int I = 500;
int LState = LOW;

void setup() {
  pinMode(L, OUTPUT);
}

void loop() {
  int gerade = millis();
  
  if (gerade - vorher >= I) 
  {
    vorher = gerade;

    LState = !LState;
    digitalWrite(L, LState);
  }
}