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The last week or two my iphone 4 started dimming it's screen to almost black whenever I lock it. Then when I unlock it I have to get to the brightness slider and move the slider to restore light to the screen.

Can anyone explain why this is happening and how to fix it?

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But when you lock the phone, the screen shuts off completely. So when does the screen start dimming? –  bassplayer7 Dec 19 '12 at 3:28
    
@bassplayer7 Good point. So it must be either when I lock the screen or when I wake it back up via the power or home button I guess. So annoying. –  dibs Dec 19 '12 at 3:58
    
I think I've run into that problem (bug) a few times before. If you haven't already, reboot your phone, and turn off "Automatic Brightness". –  bassplayer7 Dec 19 '12 at 13:48
    
@bassplayer7 That did it. Thanks. –  dibs Dec 20 '12 at 20:22
    
Great! Glad it fixed it. I'll go ahead and turn it into an answer. –  bassplayer7 Dec 20 '12 at 21:03
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2 Answers

up vote 1 down vote accepted

I've had that issue before, and it indeed seems to be a bug of sorts. As evidenced by the fact that one shouldn't have to hold their phone up to direct light, or manually adjust brightness on a frequent basis.

I would recommend starting with a phone reboot - hold down the power and home button until you see the Apple logo. This may help the situation

Next, you could also try turning off "Automatic Brightness". Open the Settings app, tap "Brightness & Wallpaper", then switch "Auto-Brightness" off.

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The algorithm for auto-brightness was adjusted significantly in iOS 6.

Rather than before where you would see an immediate change on turning on auto-adjust, now it's a more gradual process, and you can actually see the slider moving as it makes updates.

Also, another change is that the auto-adjust now works on the lock screen, so at night you won't be blinded, and in the day you can actually see the screen in day light.

Personally, I found it very annoying for about 2 weeks, and now I've adjusted to it, I find it works much better than before. If I want to manually control the screen, pointing it at a bright light causes it to brighten significantly, etc.

Finally, some sites have suggested that you can "tune" or reset it by turning auto-adjust off, setting the brightness to minimum, then turning auto back on.

Worth noting, that as I'd had to get my flashlight replaced right when iOS 6 came out, I actually assumed it had broken the ambient light sensor and I took the phone to the apple store because the auto-adjust switch didn't work as it had previously. The geniuses had no explanation for the new behaviour. I had to google it myself, and plenty of other people have complained about it.

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Informative but not an answer –  dibs Dec 21 '12 at 1:11
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