My Samsung NP740 has been running Ubuntu fine for 18 months. I did an upgrade to 14.10 and the screen brightness controls stopped working correctly. I did a wipe and fresh install and I still have the same problem.
The symptom is that the brightness is now set automatically, regardless of setting it using the controls. In a bright room, it tries to turn up the brightness automatically, although it's very hit-and-miss. Conversely, in a darker place, it tries to turn the brightness down.
The brightness control has no effect until it's turned down to zero, when the display switches off entirely (and, fortunately, comes back on again when you reverse the process).
How do I switch back from automatic to manual brightness control?