Backlight cannot be controlled after logging out and relogin

I am using Version 12.10 and Samsung 300V5A laptop.

The brightness could not be changed until I modify grub setting from /etc/default/grub and modifying the line as follows:

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

Now it works, but when I need to logout and login again, it cannot be controlled again.

The only solution was restarting...

Then I found intel-gpu-tools. Now without restarting I can write sudo intel_backlight 100 and it increases the brightness again.

Do you know why it works at first boot, but not after logout & relogin? Typing the command above in every 10 minutes after leaving computer alone is so annoying.

Thanks.