banding issue on wall I'm experiencing very ugly banding on a wall. The scene is lit with spot lamps and geometry lights (with hdr softbox textures). The wall itself is perfectly flat, but has a beveled 90° angle right above the floor. I tried to add subdivisions and support loops, that made the problem less visible, but didn't eliminate it completely. The displacement has no influence on the issue.
If I hide the geo lights (softboxes) and replace them with area lamps, no banding is visible. Unfortunately I really (really!) need those softboxes, because I have a highly reflective object in the scene, that has to catch nice and realistic reflections.
Any idea would be greatly appreciated!
Thanks for your time.
The softbox:

Edit
I couldn't reproduce the effect in a small test scene, so the problem might not even be related to the geo lights.
I panicked too early. When I stripped down the file to upload it here, I saw that I had two ground planes ontop of eachother. One of them was invisible for camera view, but was considered for glossy and diffuse bounces. This produced the banding artifacts.