Долго мучился в своё время, в итоге находил какой-то единственный рабочий вариант из 10 что были в Сети. Сейчас уже даже и не вспомню какой - через какую-то консольную утилитку. Надо будет снова заняться этим.
1. Samsung NP-R528-DA05; Intel GMA 4500M
2. uname -a
Linux folkvang 2.6.39-gentoo-r3 #6 SMP Sat Mar 3 17:24:08 EET 2012 x86_64 Celeron(R) Dual-Core CPU T3100 @ 1.90GHz GenuineIntel GNU/Linux3. ls -l /sys/class/backlight
lrwxrwxrwx 1 root root 0 Апр 1 11:35 acpi_video0 -> ../../devices/pci0000:00/0000:00:02.0/backlight/acpi_video04.
# cd /sys/class/backlight/acpi_video0/
# cat actual_brightness
7
# cat brightness
7
# cat max_brightness
7
# ls -l *bright*
-r--r--r-- 1 root root 4096 Апр 1 11:39 actual_brightness
-rw-r--r-- 1 root root 4096 Апр 1 11:39 brightness
-r--r--r-- 1 root root 4096 Апр 1 11:39 max_brightness
# echo 3 > brightnessБез изменений.
5.
# grep -iEC3 "light|^X.Org X Server|module intel" /var/log/Xorg.0.log
[ 946.992]
X.Org X Server 1.10.4
Release Date: 2011-08-19
[ 946.998] X Protocol Version 11, Revision 0
[ 947.000] Build Operating System: Linux 2.6.39-gentoo-r3 x86_64 Gentoo
--
[ 947.101] (==) Assigned the driver to the xf86ConfigLayout
[ 947.101] (II) LoadModule: "intel"
[ 947.101] (II) Loading /usr/lib64/xorg/modules/drivers/intel_drv.so
[ 947.101] (II) Module intel: vendor="X.Org Foundation"
[ 947.101] compiled for 1.10.4, module version = 2.15.0
[ 947.101] Module class: X.Org Video Driver
[ 947.101] ABI class: X.Org Video Driver, version 10.0
--
[ 947.112] (**) intel(0): SwapBuffers wait enabled
[ 947.112] (==) intel(0): video overlay key set to 0x101fe
[ 947.112] (II) intel(0): Output LVDS1 has no monitor section
[ 947.112] (II) intel(0): found backlight control interface /sys/class/backlight/acpi_video0
[ 947.128] (II) intel(0): Output VGA1 has no monitor section
[ 947.147] (II) intel(0): Output HDMI1 has no monitor section
[ 947.147] (II) intel(0): Output DP1 has no monitor section6.
$ xrandr --props
Screen 0: minimum 320 x 200, current 1366 x 768, maximum 8192 x 8192
LVDS1 connected 1366x768+0+0 (normal left inverted right x axis y axis) 344mm x 194mm
EDID:
00ffffffffffff004ca3453200000000
00120100802213780a87f594574f8c27
27505400000001010101010101010101
010101010101411c56a0500016303020
250058c2100000190000000f00000000
00000000002387026401000000fe0053
414d53554e470a2020202020000000fe
004c544e31353641543032303030007c
BACKLIGHT: 7 (0x00000007) range: (0,7)
Backlight: 7 (0x00000007) range: (0,7)
scaling mode: Full aspect
supported: None Full Center Full aspect
1366x768 60.0*+
1024x768 60.0
800x600 60.3 56.2
640x480 59.9
VGA1 disconnected (normal left inverted right x axis y axis)
HDMI1 disconnected (normal left inverted right x axis y axis)
Broadcast RGB: Full
supported: Full Limited 16:2
force_audio: 0 (0x00000000) range: (-1,1)
DP1 disconnected (normal left inverted right x axis y axis)
Broadcast RGB: Full
supported: Full Limited 16:2
force_audio: 0 (0x00000000) range: (-1,1)
HDMI2 disconnected (normal left inverted right x axis y axis)
Broadcast RGB: Full
supported: Full Limited 16:2
force_audio: 0 (0x00000000) range: (-1,1)
DP2 disconnected (normal left inverted right x axis y axis)
Broadcast RGB: Full
supported: Full Limited 16:2
force_audio: 0 (0x00000000) range: (-1,1)
DP3 disconnected (normal left inverted right x axis y axis)
Broadcast RGB: Full
supported: Full Limited 16:2
force_audio: 0 (0x00000000) range: (-1,1)
TV1 disconnected (normal left inverted right x axis y axis)
bottom margin: 37 (0x00000025) range: (0,100)
right margin: 46 (0x0000002e) range: (0,100)
top margin: 36 (0x00000024) range: (0,100)
left margin: 54 (0x00000036) range: (0,100)
mode: NTSC-M
supported: NTSC-M NTSC-443 NTSC-J PAL-M
PAL-N PAL 480p@59.94Hz 480p@60Hz
576p 720p@60Hz 720p@59.94Hz 720p@50Hz
1080i@50Hz 1080i@60Hz 1080i@59.94H7. Через Fn смена яркости не работает. Но у меня вообще без доп. настройки практически не одна комбинация через Fn не работает 
.
О, вспомнил! Чере xbacklight раньше смена работала. Только сейчас такое не проканало... Хотя в файлах actual_brightness и brightness от этого значения меняются.
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