#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 );
}