Since updating my iPhone 4S to 6.1.3 my Auto-Brightness no longer works properly.
I normally set it by going into a dark room (or putting my finger over the ambient light sensor), adjusting the brightness, then turning it on. Usually it adjusts to my environment perfectly, but since updating it no longer does.
I can hold the phone with the sensor directly under a very bright light, & the brightness bar doesn't move across like it normally does. If I'm outside, I can manually increase the brightness but if I lock the phone & put it in my pocket, when I take it out it's back down to the darkest setting & doesn't re-adjust automatically.
This issue, plus my battery life disappearing before my very eyes has me really hoping that Apple releases 6.1.4 with a bug fix VERY soon.
I have not heard about this problem as an "official" one, the problem that lots of people are facing. May be there is an issue with your software. Have you tried to restore the settings and reupdate it?