int pr=9;
int dt=100;

void setup() {
  // put your setup code here, to run once:
pinMode(pr, INPUT);
Serial.begin(9600);
}

void loop() {
  // put your main code here, to run repeatedly:
  if(digitalRead(pr)== LOW){
    Serial.println("Light!");
  }else{
    Serial.println("Dark. ");
  }

  delay(dt);

}