Unusably dim screen in KDE

[Ian Pilcher]

Fedora 14 (x86_64) on a Lenovo ThinkPad T510 an "nVidia Corporation
GT218 [NVS 3100M]" GPU.

I normally don't use my laptop's built-in display when it's at
home, so I'm not exactly sure when it started, but I suspect that
the recent update to KDE 4.6 was probably the trigger.

I can boot my system and log in to GNOME just fine.  Logging in to
KDE, however, causes the brightness of my laptop display to become
unusably dim.  This happens whether or not the laptop is running on
AC power.  The screen does return to its normal brightness momentarily
when I connect AC power, but it then returns to its dim state.

The KDE brightness controls are still set to full brightness; I can use
them to change the display from unusable dim to completely black and
back.

The only way I have found to restore the display to its normal
brightness (until I log in to KDE) is to reboot.

Anyone have any idea what might be going on?  I really am completely
unable to use KDE this way.  :-(

TIA!