Adjust Brightness 16.04

Until you find a better way, you should be able to set the brightness by editing /etc/sysfs.conf

Have a look in /sys/class/backlight to see what is there. I have (a symlink) intel_backlight but it could be radeon_b10 or something else depending on your hardware. In any case, inside it you should find a file called brightness which contains only a number that represents the current brightness. Make a note of the number! To change this value first make sure you have this package:

sudo apt install sysfsutils

then open the conf file with a text editor

sudo nano /etc/sysfs.conf

at the end of the file add a line like this:

class/backlight/intel_backlight/brightness = 4000

replace the path with the path to your brightness file (starting with class and no /), and replace 4000 with whatever number you think the brightness should be - my max brightness is 7812, so 4000 would make it about half as bright. Save the file and exit, then reboot. You will have to use trial and error to find the right brightness this way.

Here's where I learned how to do this