Blur nodes

Ok so it’s like this, I don’t know how to explain it better but I will try.
You know when you go and choose editor type (down left) and then you choose nodes and then go into compositing.
You can choose under search–>blur, bilateral blur, bokeh blur, directional blur…

I would like to make an effect like when you have some light emission and then you make some smoke trails out of it by putting a cloud texture into it.

Having a texture node (cloud), connected to blur node (directional blur I think) and then connect it to mix node.
I am trying to make that effect but the cloud texture always get’s over the whole picture and not only the light emitting part.

The final result should look something like lighting smoke trail from a emitting light but without the smoke within the render picture, something like after effects.