This is a quick post on fixing my laptops backlight. Everytime i reinstall a newer version of linux the back light is on full brightness or low brightness for my acer aspire 5741. the only fix for it on first time start up is to shut the lid and open it, this must be performed before the xorg starts.

The fix for this is to make modifications in the grub,

1. open the grub in edit mode

sudo gedit /etc/default/grub

you can use any application to edit.

1. replace the lines:

GRUB_CMDLINE_LINUX_DEFAULT=“quiet” GRUB_CMDLINE_LINUX=""

with GRUB_CMDLINE_LINUX_DEFAULT=“quiet splash acpi_backlight=vendor” GRUB_CMDLINE_LINUX=“acpi_osi=Linux”

3)save and close the editor

1. run : sudo update-grub

2. reboot your system.

This fix works for me.