#include <LiquidCrystal_I2C.h>
#define led 2

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

LiquidCrystal_I2C lcd(0x27, 20, 4);

void setup() {
  // put your setup code here, to run once:
pinMode(led,OUTPUT );
lcd.init();
lcd.backlight();
}

void loop() {
  // put your main code here, to run repeatedly:
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 ("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 );
}