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Hello! I am unable to adjust the brightness of my external monitor (iMac mid-2010) when I am using it as a secondary display to my MacBook Air (2020). When I press F1 and F2 it only changes the brightness of my MacBook Air, but not the iMac. I tried downloading the brightness slider app, but it does not solve the issue. Does anyone have a solution to this? Thank you!!
To control the brightness of the iMac display while it's in target display mode, use Displays preferences on the other Mac, or the Brightness keys on the keyboard of the other Mac.
-from this article about Target Display Mode:
Use your iMac as a display with target display mode - Apple Support
Since that article (and the feature) has now gone unsupported, I expect Apple will not fix it.
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Your only recourse may be to set the iMac brightness before you begin, then restart in Target Display Mode. If the Brightness is saved in Parameter RAM, it may be carried over to Target Display Mode.
To control the brightness of the iMac display while it's in target display mode, use Displays preferences on the other Mac, or the Brightness keys on the keyboard of the other Mac.
-from this article about Target Display Mode:
Use your iMac as a display with target display mode - Apple Support
Since that article (and the feature) has now gone unsupported, I expect Apple will not fix it.
--------
Your only recourse may be to set the iMac brightness before you begin, then restart in Target Display Mode. If the Brightness is saved in Parameter RAM, it may be carried over to Target Display Mode.
Hello again :)
Yes, when I do that, only my Macbook Air window has a brightness slider. Not the iMac. I added the picture below to show what Im seeing. Thanks again!! I really hope to find a solution! :)
Hello again,
Yes, I saw that article, but it still does not work. When I press the F1 and F2 keys on my keyboard it again only changes the brightness on my Macbook Air, and the brightness on my iMac remains the same.
And when I adjust the brightness of my iMac prior to using it as a secondary display, it automatically goes back up the moment I switch (by pressing command + F2).
Hello,
I just wanted to say that I was able to find a solution!!!
So using the iMac keyboard wirelessly does not work, but if I plug in my keyboard directly into my iMac while it is on Target display, the brightness successfully adjusts when pressing the F1 or F2 keys!! Thanks for all your help Grant :)
Use displays preferences, as you should be able to with any external display.
Hi! Thanks for your answer. However, when I go in my system preferences/display on my iMac, I can only adjust the brightness of my MacBook Air, not my iMac.
Once you have the pane for your primary display open, using the (Gather Windows) button should give you an additional pane for each external display.
so the punchline is:
"Use a F1 and F2 brightness keys on a USB keyboard directly connected to the iMac being used as a display."
Brightness of external monitor
