Cross actions between two bridges?

I am using 2 bridges. I cannot get both to work together.
I explain my project:

  • Bridge A is in the basement, connected to a motion sensor.
  • Bridge B is upstairs, connected to a color bulb.
    Both bridges are connected via ethernet. With essentials, I have acces to both.
    What I want to achieve: during the night, when a motion is detected in the basement (bridge A), I want the light upstairs (bridge B) to go on.
    Sounds pretty easy, no? but how???
    In essentials, when I want to create an action for the motion sensor, the light bulb from the other bridge does not appear in the list of devices.
    If this kind of cross action between 2 bridges is not possible, this system is no option for me…
    I hope one of you guys can help me.