So I am getting ready to install my iMac on an arm that swings out over my bed. I like to dim my screen (like on the macbook) until it turns the screen off while I am not using it. Is it possible to dim the iMac 27" until it goes off? I find that when I use the dimming button it only dims down to a low level but doesn't actually turn the backlight off. Is there an app or something out there that I can use that will turn the backlight off on demand - turning it back on with the dimmer buttons? Thanks!