GuruMania

Almost all Acer laptops running on Ubuntu Operating systems experience brightness issues as it is always set to maxmum value and it can not be reduced by the hardware key combinations eg Fn + (key).

I have experienced such problem with my machine Acer Aspire 5733 running Intel Ironlake Graphics Driver. I managed to fix the problem in several ways.

On your keyboard press ctrl+alt+T to launch the terminal emulator

Run the command sudo echo brightness | tee /sys/class/backlight/intel_backlight/brightness 
or
sudo echo brightness | tee /sys/class/backlight/acpi_video0/brightness

then enter your root password

NB: brightness is a figure for intel it ranges from 1-996 and acpi ranges from1-9.

For my case only intel_backlight works.

Editting the grub

On your terminal emulator run 

gedit /etc/default/grub 

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash ....."

and add 'acpi_osi=Linux acpi_backlight=vendor'

it would look like 

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_osi=Linux acpi_backlight=vendor"

then run

sudo update-grub

sudo reboot

to apply the changes.

All the best