#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 ();
  // put your setup code here, to run once:

}

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 (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);
  lcd.print ("       ");
  delay (100);
  // put your main code here, to run repeatedly:

}