LED lighting problem

Hello,

I have problem when I want to archive led lighting.
I create emission material. That material is visible when camera see them directly.
But when I put him behind some object he don’t affect objects around and I don’t see lighting.

Where can be problem or I need to do something else for led lighting.

This is when camera see object:

And this is when I move camera:

So why I don’t see light behind mirror? There is no obstacle.

Thank you.