@CaptainObvious
You missed my point or I didn't explained correctly.
My problem is not controling the LCD backlight, that I can do with:
analogWrite(backLight,value); // value from 0 to 255
puting 255 I get the same intensity on backlight led as when if I don't do nothing after power on Arduino.
The real problem is the intensity on the LCD digits/pixels witch after and if I used analogWrite with any value even sending 255 (maximum again I presume) I never got tha same intensity on them as after I power on Arduino and do nothing of analogWrite on backlight pin.
Conclusion if any analogWrite used on backlight led's control pin, pixels on lcd never became to have the same intensity, so anything is messing up that.
Anyway the backlight led's for the LCD RF-Robot shield are power by a transitor as you can see here on they schematic:
http://www.robotshop.us/content/PDF/dfrobot-lcd-keypad-shield-schematic.pdf