Automatically reduce brightness

The idea

When watching someone working with an iBook I noticed that the brightness automatically faded to the lowest level after a few seconds of inactivity. I think that this is a simple way to save power. I wrote a c-daemon which uses the XScreenSaver extension to check whether the user is active. If he is not, it lowers the brightness to a specific level. When he is active again, the brightness is reset to the previous level.

NOTE!

This Feature is implemented in the "gnome-power-manager" (at least from gnome 2.14) and can be used without this script (Prerequisites are needed anyway). Enable it under Gnome's Power management settings (Debian Etch: Gnome-Menu/Desktop/Preferences/Power Management) -> General-Tab -> "Dim the laptop panel when idle". "when idle" in this case means, when the gnome-screensaver sets the session idle. Change time at Gnome's Screensaver settings (Debian Etch: Gnome-Menu/Desktop/Preferences/Screensaver). If you want to see the actual content of the screen when dimmed, you should disable "Activate screensaver when session is idle".

Prerequisites

A recent kernel with the ibm-acpi driver (You should have a directory called /sys/class/backlight/ibm/ or /sys/class/backlight/thinkpad_screen/).

Installation

1. Download the brightness control daemon
2. Unpack it and chdir into the brightd directory
3. Call $ make
4. Move the brightd executable into a directory like /usr/local/bin
5. Put $ brightd -d into your ~/.Xsession (or another distro-specific startup script)
6. Change the permissions of /sys/class/backlight/ibm/brightness so that your user can write to that file

See the README for more detailled instructions and command line parameters.

Example installation for Gentoo linux and XFCE4

The following is an example which shows how to install brightd manually. The prefered way to install brightd on gentoo is to use the ebuild from bugzilla.

$ wget -o /dev/null -O brightd.tar.bz2 "http://www.pberndt.com/raw/Programme/Linux/brightd/_download/brightd-0.3_pre2.tar.bz2"
$ tar xjf brightd.tar.bz2
$ cd brightd-*/
$ make
gcc -lX11 -lXss -o brightd brightd.c
$ make install
install -Ds brightd //usr/bin/brightd
install -D brightd.1 //usr/share/man/man1/brightd.1
$ cd /etc/xdg/xfce4
$ vi xinitrc
73Gi
/usr/local/bin/brightd -s 5 -w 2 -d
<escape>:x 
$ cd /etc/init.d/
$ cat > permissions
start() {
        ebegin "Setting permissions on /sys"

        chmod g+w /sys/class/backlight/*/brightness
        chgrp wheel /sys/class/backlight/*/brightness

        eend $?
}
$ chmod a+x permissions
$ rc-update add permissions boot
$ ./permissions start

Done. Restart X to see it working. Have a look at the "-x" parameter if you intend to start the daemon from an init-script.

Example installation for Debian Sid

brightd isn't yet in the official Debian archives (an ITP was filled), but you can get precompiled binaries for unstable from Zhenech's page.

$ wget http://debian.die-welt.net/pool/main/brightd/brightd_0.1-1_i386.deb

# dpkg -i brightd_0.1-1_i386.deb

Done. Relogin into your X session and brightd will be started. You can change this and other settings by editing /etc/default/brightd.

NOTE!

Changing permissions is not needed, because the binary is installed suid-root.

Possible problems

brightd does not fade, screensaver deactivated

On my Debian Sid box, brightd can run for hours and just do nothing. This happens because it thinks the screensaver is deactivated and screen shouldn't be faded (useful while watching videos). But in fact the screensaver isn't deactivated. To solve this problem, just execute the following command before starting bright:

$ xset s default

brightd says it is fading, but does not

On my Z61m /sys/class/backlight/ibm/brightness is 0 after the laptop boots up. As long it is 0, brightd does nothing, because it thinks, brightness is already as low as possible, so I need to initialize the brightness-level before using brightd:

# echo 7>/sys/class/backlight/ibm/brightness

Other operating systems

A fairly simple but effective implementation of the same idea in Python for Windows can be downloaded here. Extract the files, edit the dimmer.pyw to match your preferences and put a shortcut to it into Autostart.