autobrightness arduino code

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

BH1750 lightMeter;

void setup() {

  //Serial.begin(9600);
  Serial.begin(115200);
  // Initialize the I2C bus (BH1750 library doesn't do this automatically)
  // On esp8266 devices you can select SCL and SDA pins using Wire.begin(D4, D3);
  Wire.begin();

  lightMeter.begin(BH1750::Mode::CONTINUOUS_HIGH_RES_MODE_2);
  Serial.println(F("BH1750 Test"));

}
int a = 0;
int addto = 1;

void loop() {
  //Serial.print("Light: ");
  Serial.println(lightMeter.readLightLevel());
  //Serial.print(" lx ");
  //Serial.println(a);
  a= a +addto;
  if(a == 254){addto = -1;}
  if(a == 0){addto = 1;}
  delay(140);
}