#include <LiquidCrystal_I2C.h>
#define LDR_PIN A0
const float GAMMA = 0.7;
const float RL10 = 50;
LiquidCrystal_I2C lcd(0x27, 16, 2);
void setup() 
{
  pinMode(LDR_PIN, INPUT);
  lcd.init();
  lcd.backlight();
}
void loop() 
{
  int val = analogRead(LDR_PIN);
  float v = val / 1024. * 5;
  float r = 2000 * v / (1 - v / 5);
  float lux = pow(RL10 * 1e3 * pow(10, GAMMA) / r, (1 / GAMMA));
  lcd.setCursor(0, 0);
  lcd.print("Room: ");
  if (lux > 50) 
  {
    lcd.print("Light!");
  } 
  else 
  {
    lcd.print("Dark  ");
  }
  lcd.setCursor(0, 1);
  lcd.print("Lux : ");
  lcd.print(lux);
  delay(100);
}