After installing the latest NVidia proprietary driver (version 390) using Software & Updates > Additional Drivers, it wasn't possible to change the backlight intensity/brightness of the screen.
The solution that worked for me was to run: sudo setpci -H1 -s 00:01.00 BRIDGE_CONTROL=0
.
If that solution works for you too, then you may want to make the change permanent. Otherwise, you will have to run the same command each time you power on your Macbook.
Steps to make the change permanent:
- Open "Terminal"
- Run
sudo gedit /etc/rc.local
- Enter: