I have a simple lighting scene set up, with some refractive and reflective materials. Rendering it with the Physically Based renderer, and 1 in the Diffuse Limit. Everything works the way I expect it to, but once I add a Half sphere with a Environment Box material applied to it (the sphere is set to Phantom in the render options), the sphere is still included in the GI calculation and light bounces off of it. Is there a setting somewhere that makes the sphere only contribute to reflections/refractions, without getting light bounces from other objects?