I came here for a different reason, but these xorg additions allow me to have backlight control with my Lenovo Y450 laptop with GT 130M graphics. I learned of this after submitting a bug report with ubuntu and googling the "RegistryDwords" stuff that was suggested there
Originally Posted by danix
For those experiencing problems with backlight controls, can you please try adding the following line to /etc/X11/xorg.conf in the "Device" section for your GPU:
Option "RegistryDwords" "EnableBrightnessControl=1"
Then restart X and see if brightness controls work.
If they do, please post an nvidia-bug-report.log along with the make and model of your laptop. Thank you.