How to setup LDR'S

Using Arduino Sensors
1

Hello, everyone! I would like to know what is the best method to calibrate sensor LDR and how i find the values for sensitivity and threshold? Thank very much

2

This might help

3

I made an LDR-based Luxmeter for my sons car headlights..
calibrated by comparison with the BH1750FVI

my code

/*  
 *   Running pr. 20.11.17
 *   calculate Rldr first  -> Then   Rldr * x^-1.6 
 *   R ser =  6k8
  The circuit: 2lines 16 char LCD panel
   LCD RS pin to digital pin 2
   LCD Enable pin to digital 4
   LCD D4 pin to digital pin 5
   LCD D5 pin to digital pin 6
   LCD D6 pin to digital pin 7
   LCD D7 pin to digital pin 8
   LCD R/W pin to ground pin 3
   LCD VSS pin to ground
   LCD VCC pin to 5V
   10K resistor:
   ends to +5V and ground
   wiper to LCD VO pin 2k2 pot

  http://www.arduino.cc/en/Tutorial/LiquidCrystal

  Circuite runs from 3*1,5V AA batteries
  resistors for battery check 47k/12k , ref 1.1V => 5V returns analog read 948
*/
#define Rsel 3
#define Enable 4
#define Db4 5
#define Db5 6
#define Db6 7
#define Db7 8

#define vpin A0
#define s1pin A6   // !!!! this is for the pro mini , Change if using UNO

#include <LiquidCrystal.h>
LiquidCrystal lcd(Rsel, Enable, Db4, Db5, Db6, Db7);
unsigned int v1, i ; // voltage1, sensor1
float battery, Lux,Rldr,s1;

void setup()
{
  Serial.begin(115200);
  //Battery check
  analogReference(INTERNAL); // 1.1V
  analogRead(vpin); delay(300); analogRead(vpin);
  v1 = analogRead(vpin);

  analogRead(s1pin); // dummy read
  lcd.begin(16, 2);
  lcd.print("Batteri : ");
  battery = v1 / 193.0;
  if (battery > 3.5)
  {
    lcd.print(battery, 1);
    lcd.print(" V");
  }
  else lcd.print("low !");
  lcd.setCursor(0, 1);
  lcd.print("Lys : ");
  analogReference(DEFAULT); // back to supply current
  analogRead(s1pin); delay(100);
  analogRead(s1pin); delay(100);
}

void loop()
{
  s1 = 0;
  for (i = 0; i < 20; i++)   s1 = s1 += analogRead(s1pin);
  s1 = s1/20.0; 
  Rldr= 68.0*(1023-s1)/s1;
  Lux = 200000.0*pow(Rldr,-1.6);
  Serial.println(Lux);
  lcd.setCursor(6, 1);
  lcd.print(Lux,0);
  lcd.print(" Lux  ");
  delay(999);
}
4

If you want to measure whether it's dark outside, or if a light is on or off, an LDR will do fine.

If you want to measure lux, get a lux meter, such as the TSL2591 (or the older TSL2561).