While in the lowest setting of windlight Invisible objects become visible. (exp) The Invisible Katana that is attached to my hand while the Katana is Sheathed is visible. when the Katana is drawn. the invisible prims set on the blade (emitters) are visible.
While in the Mid setting You can alos see the same as above but can be corrected by un-ticking the atmospheric shading box. This however cannot be done in the Low setting as the box is grayed out..