I wrote a quick and dirty script that turns on and off ATI Radeon LCD backlight by monitoring DBUS events to detect the activation and deactivation of GNOME screensaver. It requires the radeontool package to be installed and it needs to be set with suid flag (i.e. chmod u+s /usr/sbin/radeontool). Please feel free to launch the following script when your GNOME session starts:

#!/bin/sh

if [ "x`pgrep -of 'radeon-watch'`" != "x$$" ]; then

    exit 1

fi

radeontool dac on

radeontool light on

{

dbus-monitor --session --monitor "type='signal',path='/org/gnome/ScreenSaver',interface='org.gnome.ScreenSaver'" | while read -r EVT; do

    echo "$EVT" | grep -qi "SessionIdleChanged"

    if [ "$?" = '0' ]; then

        read -r EVT_VAL

        echo "$EVT_VAL" | grep -qi "true"

        if [ "$?" = '0' ]; then

            radeontool dac off

            radeontool light off

        else

            radeontool dac on

            radeontool light on

        fi

    fi



    echo "$EVT" | grep -qi "AuthenticationRequestBegin"

    if [ "$?" = '0' ]; then

        radeontool dac on

        radeontool light on

    fi



    echo "$EVT" | grep -qi "AuthenticationRequestEnd"

    if [ "$?" = '0' ]; then

        radeontool dac off

        radeontool light off

    fi

done

} &

Please note that I tested this script with my old ThinkPad X31, so you might not need this script if you have the recent laptop or you are using other video chipset.