5K iMac Boot Camp'd into Windows 10. Connected a Thunderbolt Display as a second screen. How do I control brightness for this secondary screen? It's a bit bright at the moment.
iMac Line (2012 and Later)
That's interesting: the C:\Windows\System32\runas.exe /trustlevel:0x20000 AppleControlPanel.exe command brought up a brightness control that *only* controls the secondary Thunderbolt Display. Was that the intention? If I pin that to my taskbar and close and try to re-launch if from taskbar, it comes up with that "You may not have privileges to change the startup disk" message again, unless I go into the shortcut properties and add "C:\Windows\System32\runas.exe /trustlevel:0x20000 AppleControlPanel.exe" and "run as Administrator."
That's interesting: the C:\Windows\System32\runas.exe /trustlevel:0x20000 AppleControlPanel.exe command brought up a brightness control that *only* controls the secondary Thunderbolt Display. Was that the intention? If I pin that to my taskbar and close and try to re-launch if from taskbar, it comes up with that "You may not have privileges to change the startup disk" message again, unless I go into the shortcut properties and add "C:\Windows\System32\runas.exe /trustlevel:0x20000 AppleControlPanel.exe" and "run as Administrator."
That's interesting: the C:\Windows\System32\runas.exe /trustlevel:0x20000 AppleControlPanel.exe command brought up a brightness control that *only* controls the secondary Thunderbolt Display. Was that the intention?
No. The standard method should allow either display (based on focus) to be controlled independently.
If I pin that to my taskbar and close and try to re-launch if from taskbar, it comes up with that "You may not have privileges to change the startup disk" message again, unless I go into the shortcut properties and add "C:\Windows\System32\runas.exe /trustlevel:0x20000 AppleControlPanel.exe" and "run as Administrator."
Is there a Service defined on your Mac which uses the same binary? If yes, check if it uses the System Account?
If your cursor is on the second Display, do your Brightness keys on Keyboard work properly?
Can you define a new service using AppleControlPanel.exe and let it run as a System Administrator?
"An error occurred while trying to access the startup disk settings. You may not have privileges to change the startup disk. Make sure you have administrative privileges and try again."
You can try re-installing BC drivers. Also, check in Services if you have a AppleControlPanel.exe. You can manually start it using
C:\Windows\System32\runas.exe /trustlevel:0x20000 AppleControlPanel.exe
I booted back into MacOS and everything seems fine there. (F1 and F2 change brightness on the display that mouser cursor is positioned on.) But back in Windows 10 F1 and F2 only work on the iMac display.
This is the expected behavior in macOS and Windows. A 5K iMac does allow hot-plugging TB.
Also, see if
How to reset the System Management Controller (SMC) on your Mac - Apple Support
Reset NVRAM or PRAM on your Mac - Apple Support
help.
Can you enable the Ambient Light Sensor setting on this screen and test?
Can you check the Night Light Settings?
Doesn't seem to be edit-able.
No, F1 and F2 (brightness keys) only change the brightness on the iMac display wherever the cursor happens to be.
Also the Change brightness slider in the Windows Display settings are greyed out and un-slide-able.
I also tried to open the Boot Camp control panel and got this message:
"An error occurred while trying to access the startup disk settings. You may not have privileges to change the startup disk. Make sure you have administrative privileges and try again."
I booted back into MacOS and everything seems fine there. (F1 and F2 change brightness on the display that mouser cursor is positioned on.) But back in Windows 10 F1 and F2 only work on the iMac display.
Use an existing Service (for example the Apple Mobile Device Service) and replace the executable name with AppleControlPanel.exe and test. If it does not work as expected, replace the executable value with the previous name/path.
How? That checkbox is greyed out too.
"Turn on now" makes both displays tungsten-y.
Indeed, it does.
https://support.microsoft.com/en-us/help/4027563/windows-10-set-your-display-for-night-time
Let me check if the Display Port behavior is the same as TB.
In Services I see Apple Mobile Device Service, Apple OS Switch Manager and Apple Time Service.
control brightness on Thunderbolt Display connected to 5k iMac?
