struct LdrState {
  bool isHigh;
  const byte ldrPin;
  const byte ledPin;
};

struct LdrState ldrs[] { {false,6,10}, {false,7,11}, {false,8,12}, {false,9,13} };

void setup() {
  // put your setup code here, to run once:
  for (auto &ldr : ldrs) {
    pinMode(ldr.ledPin,OUTPUT);
    pinMode(ldr.ldrPin,INPUT);
  }
  Serial.begin(9600);
}

void loop() {
  // put your main code here, to run repeatedly:
  for (auto &ldr : ldrs) {
    // if ( !digitalRead( ldr.ldrPin ) && !ldr.isHigh) { // Reverse logic (!)
    if ( digitalRead( ldr.ldrPin ) && !ldr.isHigh) {
      digitalWrite( ldr.ledPin, HIGH);
      ldr.isHigh = true;
    }
    else if (ldr.isHigh) {
      digitalWrite( ldr.ledPin, LOW);
      ldr.isHigh = false;
    }
  }
}