The Sleep Indicator Light (SIL) on your MacBook, MacBook Air, and MacBook Pro has different behaviors based on the state of your Mac. These behaviors also occur on some iMac, Mac mini, and Mac Pro models, though not all Macs have a SIL.
After you press the power button
Every time you turn on your Mac, it performs various hardware checks, known as a Power-On Self-Test (POST).
If the SIL flashes one or more times after you turn on the computer, and the pattern repeats after a brief pause, the computer may not have successfully passed POST.
- If your computer has hardware issues during POST, it might use a combination of audible tones and blinking SIL behavior to communicate POST issue codes.
- To find the cause of a POST issue, see Intel-based Mac Power On Self Test RAM error codes.
When you press the power button to turn on the computer, the SIL also turns 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 turns on and the SIL turns off simultaneously.
On Mac mini models from 2011 and newer, the SIL stays on when the computer is powered on.
During operation or display sleep
While the computer is operating, the SIL remains off. If the display turns off but the computer is still on, the SIL turns on and does not blink. It remains like this until the display turns back on, at which time the SIL turns off again.
On Mac mini models from 2011 and newer, the SIL remains on when the computer is operating.
You can turn on Display Sleep by pressing Control-Shift-Eject. To change your Display Sleep settings, drag the 'Turn display off after' slider in the Energy Saver pane of System Preferences.
When your Mac sleeps, the SIL pulsates on and off slowly. On Mac mini models from 2018, the SIL stays on when the computer is in sleep. You can customize your Mac's sleep behavior in the Energy Saver pane of System Preferences.
On Mac notebook computers, if the battery is completely depleted and the computer goes into Safe Sleep, the SIL doesn't illuminate at all.
During shut down
When you choose the Shut Down command, macOS first turns off the GPU. This turns the display off. When the display turns off, the SIL turns on. During the few seconds of shutdown, but before power is removed from the main logic board, the SIL remains on and will not blink. When the computer is fully shut down, the SIL turns off.
On Mac mini models from 2018, the SIL turns off when the computer is fully shut down.
- You can use the SIL as a diagnostic visual to determine whether the computer is getting power at startup.
- If the SIL of a MacBook Air (Original, Late 2008, or Mid 2009) flashes five times when starting up or after waking from sleep, and the pattern repeats after a brief pause, the computer's battery may require service.