HDMI link/picture detector

Hi,

I have a projector and some RGB lights that shine on the wall while it's not in use. These lights are manual at the moment but I'd like to automate them.

Is there any device that I could connect to the HDMI cable to detect when the projector has an active HDMI link with the source and if the current picture isn't just black?
I've tried Googling but I'm not really sure what to search for. I suspect such a device doesn't exist.

I have other ideas if this can't be done such as controlling the projector from the same system as the lights (IR emitter) but I'd like to do the black detection on the picture if possible.

Maybe you could use control board from monitor, and use back light driver enable signal.
That is only idea I have...