I want to clarify something for myself. on screen brightness there's the adjustment bar and then the checkbox for " auto". does the auto setting override the brightness bar setting?
Auto brightness is an option that allows the phone's sensors to detect ambient light, and then adjust the screen brightness accordingly. I can't think of a source off the top of my head, but it has been shown to cause wakelocks, which the drain the battery..
It doesn't override what you have set as the brightness on the slider, the brightest it will get is however high you set it.