I am running my Mac mini with my HDMI on my 55" monitor. If I have the max resolution on, the top panel isn't visible and the screen is really bright. When I decrease the resolution so that the panel is visible, the screen dims. I use a solar powered Logitech keyboard for Macs and the brightness buttons don't work, but the volume buttons do. I can't find a solution anywhere, because most of the dimming problems happen on laptops.