Comment 89 for bug 261721

If it isn't a Dell laptop, it isn't the same bug, file a new bug report. If it's exactly the same cause, i.e. brightness function keys reporting a down but not an up, then the solution will be similar but laptop vendor, possibly even laptop model, specific. This bug is treating Dell laptops with this issue. If yours is not a Dell laptop, then file a separate bug report.

https://help.ubuntu.com/community/ReportingBugs