I connect my 27inch Apple LED Cinema display to my iMac 2011 – somehow i can’t control the brightness on my 2nd monitor. There is no option for me to control the brightness on the 2nd monitor, the brightness only appears in the primary monitor.
How did i fix it?
I download a tool to reset the 2nd monitor http://download.info.apple.com/Apple_Hardware_Test/EDID_Reset_Tool.dmg
After you run the tool, power cycle your 2nd monitor, then you will see it brightness control option.
Hope it helps.