Comment # 12 on bug 798308 from Egbert Eich

Maybe to word Alex' question a little more for a non-developer:
The monitor that doesn't light up is an external one connected thru DP.
Now the external monitor has different power states, the 'on' state is usually
signalled by a green light. Any suspended state is signalled by an amber light.
Also, when the display comes on, the backlight needs to come on. Even with a
fully black screen you usually see the backlight - especially when the ambient
light is dimmed.

Koenraad, 
- can you check which color the monitor power light has when the monitor is 
  expected to be on?
- can you check if the backlight is on (although the screen appears to be
blank)?
- In this state, please run 'xrandr --verbose' and attach the output.

Thanks!