As Paul "face_off" suggested I'm copying my question here:
Sorry i didn't find how to make a double sided material

I have a plane with a texture on opacity which emits light. (see attachement)
The problem is that it not emits light from both sides of the polygon.
In modo you just turn "double sided" and it's done.
How to do that in Octane?
Doubling the polygons and flipping the normals is not a memory effective solution when you have heavy geometry.
Do you plan adding a feature for that?
Thanks!
Friendly
Maciej Frolow
http://www.maciejfrolow.com