#include <Wire.h>
#include <LiquidCrystal_I2C.h>

#define LED 2

const float GAMMA = 0.7;
const float RL10 = 50;

LiquidCrystal_I2C lcd(0x27, 20, 4);

void setup() {
  pinMode(LED, OUTPUT);

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

void loop() {
  int analogValue = analogRead(A0);
  float voltage = analogValue / 1024.0 * 5.0;
  float resistance = 2000 * voltage / (1 - voltage/ 5);
  float lux = pow(RL10 * 1e3 * pow(10, GAMMA) / resistance, 1.0 / GAMMA);

  lcd.setCursor(2, 0);
  lcd.print("Cahaya: ");
  if (lux > 50) {
    lcd.print("Terang!");
    digitalWrite(LED, LOW);
  } else {
    lcd.print("Gelap ");
    digitalWrite(LED, HIGH);
  }
  lcd.setCursor(0, 1);
  lcd.print("Lux: ");
  lcd.print(lux);
  delay(500);
}