When I render with Direct Light Sampling on or off, I get quite different results for the scene below. It is the default cube with a simple glossy material, lit by a HDRI:
So, which is the correct result?
Since I can't say whether this is a render, exporter, or Blender issue, or ultimately there is something wrong with my scene, I have attached the .blend file for you to give it a try. The HDRI is #7 from this pack, but I'm pretty sure any similar set-up would do.
For a reference, I'm using is LuxRender_CVS_20120111_64bit_OpenCL with Blender r43433 x64 on Win7 x64.