How to get Monitor/Display power status?

I'd like to write a simple daemon that monitors whether or not the display is currently powered up. This is for a digital signage application, and we need to know if somebody has powered off the display, even though the Mac is still running along just fine.

I'm having a hard time finding the proper notifications (if they even exist) to listen for.

Any ideas? Or do I have to implement some kind of external solution?

Thanks in advance,

Chuck