This thread might be of help...
I remember seeing a post about how to get the screen illumination to not dim when you take it off the power cord but Im having trouble finding it. Any help?
If you click on IBM access from the start menu, then click on the manage your display option. From there click on lcd display settings. If you keep it on high, it shouldn't dim after you unplug it. You can always do this as well after you unplug and get the screen to brighten I believe.
If you're running Windows and have Power Manager installed, you can use it to customize your power settings, including but not limited to, the display brightness of the screen in plugged-in and battery mode.
Have a nice weekend.