It is a very common problem with linux users - not being able to control the brightness..
1. First Option ls /sys/classes/backlight
if it shows you intel_backlight sony_backlight
then you can choose anyone and check
ls intel_backlight it will return brightness max_brightness actual_brightness
like options. try echo 5 > brightness
2. Use xrandr first identify your ldvs and then change the value,, but it will not change the value at the hardware level... 3. use xgamma -gamma .30 it will change the gamma
4. If you are nvidia users.. and if you are not able to control the brightness... download latest nvidia drivers and follow the steps carefully first : uninstall current nouveau kernel (which is default used by system of nvidia) using apt-get remove nvidia*
then go to terminal mode ctrl+alt+f1 then kill x-server (default desktop graphics mode) service lightdm stop then sh NVIDIA-DRIVER.run now reboot and enjoy.
5, else try changing the grub /etc/default/grub CMDLINUX line to include quite splash acpi_backlight=vendor if you are able to see 2 options in ls /sys/classes/backlight if none of the above options work for you try installing xbacklight | redshift