2IC LCD PCF8574T

i have just started programming my Arduino Uno and working through basic programs.
i have played around with my 2IC LCD PCF8574T displaying the Hello World!

now i have just completed making happy faces. my question i need help with is why i cannot adjust the back light, i can only turn it on and off.

the I2C board has a jumper which keeps the BL on all the time and i have read articles on the web were i need to remove this. that done the program does not turn it on or off.

//-----------Header-------------

//1st Arduino experiment LCD 
// by craig Wilson 22/05/2015
#include <Wire.h> 
#include<LiquidCrystal_I2C.h>
LiquidCrystal_I2C lcd(0x27, 2, 1, 0, 4, 5, 6, 7, 3, POSITIVE);
byte smiley[8] = {
  B00000,
  B01010,
  B01010,
  B00000,
  B00100,
  B10001,
  B01110,
  B00000
};
int z=1;
//-----------setup--------------
void setup() 
{
 // ------- Quick 3 blinks of backlight  -------------
  for(int i = 0; i< 3; i++)
  {
    lcd.backlight();
    delay(1000);
    lcd.noBacklight();
    delay(1000);
  }
  lcd.backlight(); // finish with backlight on 
  // put your setup code here, to run once:
lcd.begin(16,2);
lcd.createChar(0, smiley);
lcd.clear();
//lcd.setcursor(0,0);
}


//------------Loop---------------
void loop() {
  // put your main code here, to run repeatedly:
z=z+1;
//lcd.setCursor(0,1);
lcd.print(char(0));
//if(z==2)z=0;
delay(50);
}