(TDE 3.5.13.1) The default monitor setting on my laptop (HP G72) are not very clever. After a reboot, the screen appears to lack contrast and brightness: it appears that one is looking at it through the evening mist at dusk. All attempts to remedy this using System Settings were ineffective. The Brightness and Gamma tab only provides facility to adjust Gamma. When experimenting with Gamma, pressing the apply button causes a crash (on attempting to get a backtrace, the post mortem routine responded with that the stack was corrupt and no useful pm information could be gleaned. [/tmp/kde-jmdh/drkonqihlXzND.tmp:1: Error in sourced command file: No stack].

It would be more useful if there was the facility to adjust both brightness and contrast before fiddling with the gamma. When the Power Management tab is invoked, the only choice offered is to use the DPMS power save modes (whatever they are); I left that switched off. I expected to find the ability to adjust the brightness for when the system connected to the mains or when it is running on batteries. Provision is there to adjust various time constants. 

A different observation which you may like to look at is why is it necessary to sign into administrative mode every time when one changes tab in the Monitor & settings page? That makes that particular tool rather user hostile, even if it did work satisfactorily otherwise.