LXDE Forums

The "dcon-bl" part of the path is different for every video driver, and also can be changed by kernel boot parameters and module parameters.
For instance mine shows both a "acpi-bl" (which doesn't actually work) and "psb-bl" (which works)
But if I put acpi_backlight=vendor (or some other option, I forget the exact detail) then reboot, there is no psb-bl any more, but in it's place is some other name like sony-bl.

So basically, you have to look in /sys/class/backlight yourself and see what's there. If there is more than one thing there, you may have to try them all.

After having the same problem with E17 / Bodhi Linux, I wrote this:

http://code.google.com/p/bltool/

It won't work fully automatically in a lot of cases, but it has several different ways of working, and you can specify things the usual binaries and modules/plugins don't let you specify, so with a small amount of tedium you can write .bltool config file that makes it work.

Docs are a bit hard to follow, sorry. Just read the built-in help output and the comments at the top of the script (almost the same, but a little more explanation for some things)

Also note the udev rule provided in the help output. IT at least, doesn't care what video driver you use. But one further complication not mentioned in the docs is, it assumes all users are members of group video, which I thought was pretty universal but apparently is not. So you need to add yourself to group video, IF you even need to use the sysfs method of setting brightness. You MAY find you can use xrandr, which is slower, but doesn't require special permissions.

Problem for me too.

Ive just installed Ubuntu 12.10 on Tosh Sat Pro L300, and using LXDE, as a sequential upgrade from Ubuntu 10.10 (Gnome) via 11.04, 11.10 and 12.04.
I also have Unity and Gnome desktops installed. Under 10.10 I had a panel applet to adjust the brightness and this worked fine with the hardware. I don't know if F6 (brightness down) and F7 (brightness up) worked because I never used them.

Under Ubuntu 12.10 there is no brightness applet for LXDE. The brightness function in Unity doesnt work (cant remember where - saw so many alternate ways of setting preferences that my head exploded). The slider slides, but no change with the h/w. F6 and F7 don't work.

I followed some advice to
1. fix /etc/default/grub and put in acpi_backlight_vendor (but this was already in)
2. edit /home/<user>/.config/openbox/lubuntu-rc.xml and add 2 definitions for brightnessUp and brightnessDown
3. add to /usr/bin the commands brightnessUp and brightnessDown, which refer to
4. /sys/class/backlight
(instructions here: http://ubuntuforums.org/showthread.php?t=1855199&page=2 and somewhere else also by Toz)

The difficulty is that trying to control /sys/class/backlight/intel_backlight/brightness gives an i/o error...
actual_brightess contains 0, brightness contains 0 and max_brightness contains 1.
There is no alternate device type in /sys/class/backlight (the only one is intel_backlight).
intel_backlight is actually a link to /sys/devices/pci0000:00/0000:00:02.0/drm/card0/card0-LVDS-1/intel_backlight

So none the wiser...

Any good ideas?

Just one extra comment - I also have a file in /sys/class/backlight/intel_backlight called actual_brightness which contains 0. Writing to this file also causes an i/o error. Sounds to me like the driver for the backlight has been changed and no one bothered to tell anyone about how to drive the new design...

Every laptop is different, so adjusting the brightness or contrast on your laptop may vary from the steps provided on this page. However, understanding the process of how to adjust the brightness or contrast will help you change your settings.