const int blitzPin = 13;  // the output pin to the flash
const int resPin = 2;     // the input of the lightbarrier
int sensorValue = 0;      // set the sensor-value to zero
int verzoegerung = 100;   // delay between lightbarrier and flash


void setup() {
  pinMode(blitzPin, OUTPUT);  // setup output pin for flash
  pinMode(resPin, INPUT);     // setup input pin for lightbarrier
}

void loop()
{
   sensorValue = digitalRead(resPin);  // read the value of the barrier
   
   if (sensorValue){                   // if lightbarrier is high
     delay(verzoegerung);              // wait for a moment
     digitalWrite(blitzPin, HIGH);     // trigger the flash
     delay(200);                       // wait again
     digitalWrite(blitzPin, LOW);      // release the flash
   }
}