This question is somewhat related to this question: Brightness is reset to Maximum on every Restart
Basically, I modified
/etc/rc.local to set the brightness, as detailed in this answer, so on startup the brightness does get set to the correct value. However, when I suspend my laptop and wake it up, or simply close the screen and reopen it, the brightness gets reset to the maximum.
My machine runs Ubuntu 14.04 + Gnome 3. The machine is a Thinkpad X1 Carbon.
What's the solution?