This isn't your typical water damage story.
One side of my 2007-model, pre-Unibody laptop got damp from rain in a backpack yesterday. When I opened it, the left quarter of the screen had a splotch of water damage.
The damaged area is brighter and more vibrant than the rest of the screen!
The screen has seemed dim for most of the laptop's lifetime. Not long after its first birthday I even disassembled the screen looking for the problem. I found a blown capacitor and supposed a backlight power issue, but later discovered that wasn't the case.
Now this seems to confirm it's some kind of optical effect. But what? I know plenty about optics and this doesn't make sense. The water must be filling a gap and providing better coupling between two layers, but there's no brightening if I press lightly on the screen. There's a little thin-film interference at the edges of the water layer where it tapers off. So the water layer is doing something.
The laptop will be fine in a few days; the water seems to be evaporating out through the screen. But I'm suffering this physics mystery.