const int ledPin = 13;
const int luxPin = A0;
const float GAMMA = 0.7;
const float RL10 = 50;

void setup()
{
    pinMode(ledPin, OUTPUT);
    pinMode(luxPin, INPUT);

    digitalWrite(ledPin, LOW);
}
void loop()
{
  int analogValue = analogRead(luxPin);
  float voltage = analogValue / 1024. * 5;
  float resistance = 2000 * voltage / (1 - voltage / 5);
  float lux = pow(RL10 * 1e3 * pow(10, GAMMA) / resistance, (1 / GAMMA));

  if (lux > 200)
  {
    digitalWrite(ledPin, HIGH);
  }
  else
  {
    digitalWrite(ledPin, LOW);
  }
}