Spiral Blur very dark

Hello there,
I hvae been working with the spiral blur the last days and got it working, but it does not behave how I would anticipate.
When throwing the material (simplest setup possible) into the scene, the material is blurring - but is incredibly dark. Even whren setting the blur distance to a value of 0, where the material doesn’t blur at all, the material ist still that dark. Can someone point out if I am using the node wrong or is it a bug/limitation (because my scene is to dark?!).
There are some screenshots: First a sphere with the material in the scene, second and third screenshots from the material editor. Thanks!

270682-ss2.jpg

Update: I played a bit with it around and found out that the material looks right when plugging the Result into the emissive channel - but then the material does not have any reflections.