The Ray Tracing object properties
Ray-Trace Displacement
If enabled (the default), the affected objects will be tessellated and displaced for ray tracing(19). If disabled, the 3Delight render engine will not tessellate surfaces for ray tracing, instead, it will use analytical intersection methods to keep memory usage low and will use bump-mapping to simulate the effect of the displacement (which should be enough in most cases).
Ray Bias
Specifies the minimum distance after which an intersection is considered valid in the ray tracer. This is to avoid self-intersections on ray-traced geometry.