Does an excellent job This kind of app is exactly why I made the switch from apple. At one point I had cut out a piece of car window tint  taped it to my iPhone as it was way too bright. User friendly?! Note if changing text size in the kindle app it can sometimes turn screen super bright. It's a kindle thing  just goto settings in kindle and check 'use system brightness' for some reason kindle seems to attribute the pinch or pull text resize as an invitation to over ride your system brightness and completely blind you. :)