Can't adjust brightness on my laptop

Try this.

1. Open the Terminal (Ctrl+Alt+T) and type:

   gksu gedit /etc/default/grub
   

2. Change the line:

   GRUB_CMDLINE_LINUX=""
   

   To:

   GRUB_CMDLINE_LINUX="acpi_osi=Linux"
   

3. Save the file and quit the text editor.

4. Now in the terminal run:

   sudo update-grub
   

5. Restart Ubuntu.

Based very closely on this article: living in java

I also have an ACER, but ASPIRE 4736Z. Same problem.

xbacklight, xgamma doesn't work.

Something that did work for me is redshift utility: Is there a software utility to adjust screen gamma/brightness/contrast?

https://bugs.launchpad.net/emgd/+bug/711172

Add to kernel command line:

acpi_backlight=vendor

And you are done!