In a controlled environment, like your office, you can set the brightness of your display how you want it and it'll be good for most of the time (unless you're lucky enough to have an office with giant windows). Smartphones, on the other hand, are constantly in a state of travel and will be under various different light conditions, varying from pitch darkness when you're hiding under a cardboard box to when you're under the blasting rays of the sun. For this reason, automatic brightness is an important feature of smartphones.
Sadly, the automatic brightness setting in your iPhone or your Android-based phone is terrible.
Dr. Raymond M. Soneira of DisplayMate exhaustively examined the auto-brightness settings for the iPhone 4 and several modern Android phones and found them to be useless.
"Automatic Brightness on existing smartphones is close to functionally useless because the manufacturers have not made the effort required to develop, evaluate and test the software and hardware so that they work properly and effectively," wrote Soneira. "All of the models we tested also have serious operational errors and bugs indicating how little an effort has been made to make them work (or rather not work) properly."
The problem with the iPhone automatic brightness is that the phone jacks up the brightness when it detects bright lights, but then it doesn't dim the display when things are dark again.
Android suffers from inconsistent settings that vary from manufacturer to manufacturer, with some leaving the automatic brightness cranked way too high on default, to being far too low even when outdoors in daylight. Android phones also do not offer a starting brightness slider when automatic brightness is enabled.