Adjusting brightness on 27" iMac used as external DisplayPort monitor for PC I have a Windows7 64-bit machine attached to a 27" iMac as an external displayport monitor It's working well, except I cannot adjust the brightness.

I have attached a Mac keyboard both on the Mac &amp; Windows side to gain access to the brightness controls, with no luck. As soon as I switch to display target mode, the screen jumps to full brightness, and cannot be controlled from the keyboard on either platform.

I have searched the web but have not found the answer:
http://support.apple.com/kb/HT3924
http://macs.about.com/od/usingyourmac/qt/using-target-display-mode.htm
https://superuser.com/questions/60145/how-do-i-use-a-new-27-imac-as-an-external-pc-monitor-with-full-2560x1440-resolu
I just had an issue with not being able to change the brightness on my 27inch iMac in Target Display Mode. It was at full brightness. And the brightness keys on the keyboard hooked up to the TDM Mac would not adjust it. But I found if I pressed and held Commond-F1 on that keyboard it slowly lowered the brightness. This probably won't help much if you have an issue with it defaulting to a low brightness though.

iMac 2009 High Sierra and iMac Pro Mojave.