Mac computers: Sleep Indicator Light behavior

This article details various Sleep Indicator Light (SIL) behaviors and what they mean.

Note: If your MacBook, MacBook Air, and MacBook Pro has a SIL, the following behaviors will occur. These behaviors also occur on some iMac and Mac Pro models, although not all Macs have a SIL.

SIL states and behaviors

Power-On Self-Test (POST)
If the SIL flashes one or more times after you press the power button to turn on the computer, and the pattern repeats after a brief pause, the computer may not have successfully passed POST.

  • If your computer encounters hardware issues during POST, the computer may use on a combination of audible tones and blinking SIL behavior to communicate POST issue codes.
  • To determine the cause of a POST issue, observe the SIL blinking pattern. Then, refer to the following Apple support article for more information about POST codes: Intel-based Mac Power On Self Test RAM error codes.

When you press the power button to turn on the computer, the SIL will also turn on. As the computer starts up, the SIL stays on until the processor (GPU) has initialized and the display turns on. When the GPU initializes properly, the display will turn on and the SIL will turn off simultaneously. 

Running and Display Sleep

While the computer is started and running, the SIL will remain off.


The SIL will remain off until the computer enters the Display Sleep state while running (the display turns off but the computer remains running). While in this state, the SIL turns on and does not blink. It remains like this until display turns back on, in which case the SIL will turn off again.


Note: You can enable Display Sleep via Apple () menu > System Preferences > Energy Saver, or by pressing Control-Shift-Eject.


Computer Sleep

When the computer is in the Computer Sleep state the SIL will pulsate on and off slowly. You can enable Computer Sleep via Apple () menu > System Preferences > Energy Saver.


On portables, if the battery is completely depleted and the computer goes into Safe Sleep, the SIL will not illuminate at all.



Once you choose the Shut Down command, OS X will first turn off the GPU.  This will cause the display to turn off. When the display turns off the SIL will turn on. During the few seconds of shutdown, but before power is removed from the main logic board, the SIL will remain on and will not blink. When the computer is fully shut down the SIL will turn off.


Diagnostic uses:

  • You can use the SIL as a diagnostic visual to determine whether the computer is getting power at startup.
  • MacBook Air (Original, Late 2008, and Mid 2009) Battery Diagnostic: If the MacBook Air's SIL flashes five times at power on or after waking from sleep, and the pattern repeats after a brief pause, the computer's battery may require service. For more information, refer to MacBook Air (Original, Late 2008, and Mid 2009): About the battery diagnostic.


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