(HP Pavillion laptop zv6000)
I had a power outage today at home. Got home, turned on the computer (was completely powered off all day), and now the screen brightness/intensity is comparable to when the laptop is not connected to an AC power supply. If I unplug the AC, the screen brightens to "normal". If I use the control panel settings for brightness, it gets very white washed.
Basically, it's as if the display is acting backwards in regards to whether or not AC is connected. Tired powering off/back on again. Tried unplugging AC supply. No effect.