#include <LiquidCrystal_I2C.h>

#define LDR_PIN 2
int led=13;
// LDR Characteristics
const float GAMMA = 0.7;
const float RL10 = 50;

LiquidCrystal_I2C lcd(0x27, 20, 4);

void setup() {
  pinMode(LDR_PIN, INPUT);
  pinMode(led, OUTPUT);

  lcd.init();
  lcd.backlight();
}

void loop() {
  int analogValue = analogRead(A0);
  float voltage = analogValue / 1024. * 5;
  float resistance = 2000 * voltage / (1 - voltage / 5);
  float lux = pow(RL10 * 1e3 * pow(10, GAMMA) / resistance, (1 / GAMMA));

  lcd.setCursor(0, 0);
  lcd.print("Ruangan: ");
  if (lux > 300) {  
    lcd.print("Terang !");
    digitalWrite(led,   LOW);
  } else {
    lcd.print("Gelap ");
    digitalWrite(led, HIGH);
  } 

  lcd.setCursor(0, 1);
  lcd.print("Lux: ");
  lcd.print(lux);
  lcd.print("          ");

  delay(100);
}