How to turn ambient light sensor auto-wake off

Discussion in 'iMac' started by GreatUsername, Aug 16, 2014.

  1. GreatUsername macrumors member

    Feb 4, 2013
    I have a late 2012 27" iMac and a Moshi Luna keyboard.

    Whenever my computer goes to sleep, it immediately wakes back up before going back to sleep after some time and immediately waking back up again. This continues indefinitely.

    I believe this is because the ambient light sensor detects the change in lighting as the Moshi Luna's backlighting turns off and therefore wakes the computer back up.

    Is there any way I can turn off the ambient light sensor auto-wake feature so this stops happening? I'd like to be able to actually put my computer to sleep without having to unplug my keyboard or cover the light sensor.

    Or is there something else causing this problem? I would think Apple would have worked something like this out considering all MacBooks have backlit keyboards and most third party keyboards are backlit.
  2. insane79 macrumors 6502

    Aug 20, 2008
    never heard of this feature :eek: does it actually wake up when the sensor senses movement in front of the screen?? i got a late 2012 27" iMac & i don't have this feature..
  3. GreatUsername thread starter macrumors member

    Feb 4, 2013
    It was a feature added is Mavericks and yes, it does work. It detects changes in light to act as a pseudo-motion sensor. Before I got my Moshi Luna, the feature worked as intended: I would arrive home, walk past my Mac, do something like take a shower, and when I'd come back to my desk my Mac would be awake and ready for me to use. I've also noticed it waking up when I open/close the blinds on my window and also when I turn the lights on/off.
  4. insane79 macrumors 6502

    Aug 20, 2008
    Never got this feature to work on my late 2012 27" iMac which is on 10.9.4
    I have auto brightness enables & iMac sleep setting at 15 mins with screen sleep at 1mins, screen saver is disabled but once my iMac goes to sleep it never wakes up by any lightning or me going in front of the screen :confused: My ambient sensor is working as the screen dims & gets brighter auto when i change the light moods in my room. Wonder how i can use this auto wakeup feature :(

  5. ApfelKuchen macrumors 68030

    Aug 28, 2012
    Between the coasts
    There's nothing in Apple documentation or my system preferences (10.9.4, 27" late 2013 iMac) that suggests the ambient light sensor will automatically wake the Mac. It sure doesn't work that way for me, on either of my Macs, both of which have ALS and both of which have Mavericks. The Mac in my bedroom should turn on whenever I get up to go to the bathroom if it was light-triggered.

    I'd think this article would mention the ALS, if it was a factor:

    OS X Mavericks: If your Mac won't go to or stay in sleep

    Consider this sentence in particular:
    Then there's this description of how to put a Mac to sleep:

    Your description of how it used to wake - you'd come home, do stuff (like take a shower), and it'd be awake when you returned, is inconsistent with the idea of wake-on-motion. With normal wake-from-sleep, it takes less than a second for the screen to come up. Why would it not come up instantly when the light changed? You'd undoubtedly have seen it wake before going for your shower.

    Further, it's illogical for a power-saving feature to work as you describe (any change of ambient light wakes it) - ambient light can change fairly often, but for the sake of power savings, the computer should only wake when actually needed - a key press, mouse click, etc.

    What about Wake for network access? The screen stays dark when I access my iTunes Library or HDD from the other Mac on my network, though I was able to wake the screen by using Share Screen from that remote Mac.

    The ambient light sensor is accessible from System Preferences > Displays > Automatically adjust brightness. The ALS is supposed to be deactivated if you un-check that option. Why don't you un-check it, and see if there's any impact?

    My guess is that the wake-from-sleep issue was unrelated to ambient light before you changed the keyboard, and and the situation only got worse afterwards. Follow the troubleshooting recommendations in and see what happens.
  6. GreatUsername thread starter macrumors member

    Feb 4, 2013
    Alright, so I looked up the article where I first heard about this feature:

    And I now realize that I completely misinterpreted the article's title as that was all I read when it first came out. Alright, so my computer isn't waking from light changes, now let me be more specific about the problem:

    When my computer goes to sleep and the screen goes dark, at first the keyboard is still lit up, my second monitor is still turned on, and so are my external speakers. Then after about 20 seconds, they all turn off before turning back on just a moment later. The Mac itself isn't waking up, but everything connected to it is. I suppose it's just been a series of strange coincidences that my Mac would happen to wake up everything just as I'm there to see it.

    When my computer is sleeping, I'd really rather not have a monitor and keyboard still glowing, while my speakers are also creating a persistent hiss in the room.

    Now knowing that it's not the ambient light sensor keeping it awake, what else could be causing this? I turned off "Power Nap" and "Wake for network access" in Energy Saver and "Automatically Adjust Brightness" under Displays and the problem persists.

    At least it doesn't take too long for the computer to start up because it looks like I'm going to have to shut it completely off when I'm not using it from now on.
  7. VictorMX macrumors newbie


    Dec 27, 2015
    Well i have a 2012 iMac with Yosemite, and when i arrive to my offices at 7pm its all dark and when i turn the lights on, the iMac awakes, keyboard and mouse off, this wasn't a problem until know because my dad goes to the office some times at 7 or 8 pm and the same thing happened, any one having a solution for this ?

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