Thank you for your reply; however, this does not address the issue at all.
The screen dimming has nothing to do with the standard power and brightness settings. It occurs at any time when the the computer is running on battery power, not only when the computer switches from AC to battery, and the screen both BRIGHTENS and DIMS on its own but ONLY if it is running on battery.
This is an issue with Intel drivers (I have 3345). I do not experience this problem if I uninstall the Intel drivers and use the generic PnP drivers.