Motorola Droid :: Screen Brightness Adjusting Automatically

Until now I had my screen set to auto brightness.First, +1 to those who said in other threads that the screen looks even better when you turn that off and put brightness all the way up.But my question here is why, on auto brightness, the screen sometimes increased or decreased brightness when I was using it. It happened all the time. The only thing I can rule out as the cause was time delay, because sometimes it happened as I was typing or just after, and sometimes it would happen after a delay. I think it must be connected to either orientation, or movement, or brightness sensor detecting the ambient light, or something.If I could figure out how to make it stop doing that I would go back to auto-brightness.