I was always getting ‘54612 lux’ measurments. It was mystery, until I found out, that I had to connect my SCL and SDA pins to dedicated 20th and 21st pins on Arduino MEGA 2560.

BH1750 light intensity module test.ino

/*
  Example of BH1750 library usage.

  This example initalises the BH1750 object using the default
  high resolution mode and then makes a light level reading every second.

  Connection:
  VCC-5v
  GND-GND
  SCL-SCL(analog pin 5)
  SDA-SDA(analog pin 4)
  ADD-NC or GND
*/

#include <Wire.h>
#include <BH1750.h>

BH1750 lightMeter;

void setup() {
  Serial.begin(9600);
  lightMeter.begin();
  Serial.println("Running...");
}

void loop() {
  uint16_t lux = lightMeter.readLightLevel();
  Serial.print("Light: ");
  Serial.print(lux);
  Serial.println(" lx");
  delay(1000);
}