為什麼iMac在睡眠狀態下會半夜自動點亮？

我的iMac不用時是處於睡眠狀態的，但是偶然的幾次半夜醒過來，發現它自動點亮了，持續大概兩秒又變回黑屏。而且再等一會又兩次點亮。網上說是因為設置了『喚醒以供網路訪問』，我去掉了之後問題依舊。請問大家有遇到相同的情況嗎？要如何解決呢？

下面是我的設置及系統版本

--- 2015.12.26 更新 -------------------------------

@王飛 這是不是表示有後台任務的時候它就會醒著？那有可能是自動更新。

教你一個命令，自己去排除下，

pmset -g assertions
2015-12-26 13:31:32 +0800
Assertion status system-wide:
BackgroundTask 0
ApplePushServiceTask 0
UserIsActive 1
PreventUserIdleDisplaySleep 0
PreventSystemSleep 0
ExternalMedia 1
InternalPreventDisplaySleep 1
PreventUserIdleSystemSleep 0
NetworkClientActive 0
Listed by owning process:
pid 61(powerd): [0x000000040008012c] 89:15:32 ExternalMedia named: "com.apple.powermanagement.externalmediamounted"
pid 61(powerd): [0x0004e668001001ed] 00:03:48 InternalPreventDisplaySleep named: "com.apple.powermanagement.delayDisplayOff"
Timeout will fire in 294 secs Action=TimeoutActionTurnOff
pid 113(hidd): [0x0004e5540009060a] 00:08:24 UserIsActive named: "com.apple.iohideventsystem.queue.tickle"
Timeout will fire in 867 secs Action=TimeoutActionRelease
Kernel Assertions: 0x12c=USB,BT-HID,THNDR,MAGICWAKE
id=500 level=255 0x20=THNDR mod=12/26/15, 1:24 PM description=NHI0 owner=AppleThunderboltHAL
id=501 level=255 0x20=THNDR mod=12/26/15, 1:50 AM description=NHI1 owner=AppleThunderboltHAL
id=502 level=255 0x20=THNDR mod=12/26/15, 1:24 PM description=NHI2 owner=AppleThunderboltHAL
id=504 level=255 0x4=USB mod=1/1/70, 8:00 AM description=com.apple.usb.externaldevice.00400000 owner=LaCie Hard Drive USB
id=505 level=255 0x4=USB mod=1/1/70, 8:00 AM description=com.apple.usb.externaldevice.01400000 owner=USB audio CODEC
id=506 level=255 0x4=USB mod=1/1/70, 8:00 AM description=com.apple.usb.externaldevice.02400000 owner=USB audio CODEC
id=508 level=255 0x4=USB mod=1/1/70, 8:00 AM description=com.apple.usb.externaldevice.00700000 owner=P9233 Desktop Drive
id=510 level=255 0x8=BT-HID mod=1/1/70, 8:00 AM description=com.apple.driver.IOBluetoothHIDDriver owner=AppleHSBluetoothDevice
id=511 level=255 0x100=MAGICWAKE mod=12/25/15, 2:53 PM description=en1 owner=en1
id=531 level=255 0x8=BT-HID mod=1/1/70, 8:00 AM description=com.apple.driver.IOBluetoothHIDDriver owner=AppleHSBluetoothDevice
id=533 level=255 0x4=USB mod=1/1/70, 8:00 AM description=com.apple.usb.externaldevice.00600000 owner=USB5534B
id=534 level=255 0x4=USB mod=1/1/70, 8:00 AM description=com.apple.usb.externaldevice.00200000 owner=USB2134B
id=535 level=255 0x4=USB mod=1/1/70, 8:00 AM description=com.apple.usb.externaldevice.01100000
Idle sleep preventers: IODisplayWrangler