Currently Being ModeratedNov 27, 2012 7:11 AM (in response to dietrichate)
Make sure the display brightness controls are set properly. Use the brightness buttons on the side of the display or choose Apple > System Preferences, and click Displays.
If a portion of the screen remains dim after the display has warmed up and the white
LED on the front of the display is flashing a repeating pattern, contact an Apple Authorized Reseller or Service Provider.
This is from the manual on the Apple Support Site.