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I have a MacBook Air Late 2010. I notice that sometimes when I press the decrease brightness button, it causes the brightness to increase and only after subsequent presses it starts to actually reduce the brightness (from this now higher brightness setting).

I was just wondering why this happens, and if it's related at all to an ambient light sensor similar to the one that the iPhone has.

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3 Answers 3

The Air does have an ambient light sensor. Try disabling it in the Displays System Preferences pane and see if it fixes the problem.

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If I go into System Preferences > Displays, I don't see any such setting. –  Senseful Feb 20 '11 at 4:00
    
@Senseful: screen shot from Apple here: support.apple.com/library/APPLE/APPLECARE_ALLGEOS/HT4293/… –  Nathan Greenstein Feb 20 '11 at 15:01
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What Nathan is suggesting is that the Ambient Light Sensor has dropped the brightness down below the set value. When you press a brightness setting button, it is reset to the statically defined value, which is perhaps brighter than what the sensor dimmed it to. So it gets brighter to the last setting, then dimmer as you press it. –  Jason Salaz Apr 21 '11 at 17:36

If the Air is not used for a while, it will dim the screen to save power. If it detects any user action, such as pressing the "decrease brightness" key, it will return the screen to its original brightness, and taking that one notch down because you've pressed the key will still be brighter than it was.

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I'm aware of the screen auto dimming, but this is not when I experience this effect. Usually I will be using the computer right before I press the brightness button, meaning that it shouldn't be in auto-dim mode. –  Senseful Feb 20 '11 at 8:00

You might need to "recalibrate" your light sensor. I do this by placing my thumb over the camera area to cover the light sensor. Then I max out the brightness. It seems to work because afterwards the brightness control works as its supposed to.

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