Originally Posted by JonWW

Try a dbus-monitor command, it will save you battery as you will not be running a point less loop all the time doing something that hardly ever needs to be done.

Code:

#!/bin/sh

dbus-monitor --system type='signal',interface='com.nokia.mce.signal',member='display_status_ind' | while grep -q "display_status_ind"
do
  echo 160 >/sys/class/backlight/acx565akm/brightness
done

This code will only ever activate when the brightness changes (hopefully), I have not been playing around with /etc/mce/mce.ini so cannot say how well it will work for you.