stewer, would you apply that to a sphere that encloses the scene, and if so would you still need to use lights (which hdri images normally produce)? The HDRI map here is used for reflection, not illumination. It's a popular confusion, 99% of the time when someone says "HDRI" he/she really means image based lighting. Not here - here HDRI is just that - a high dynamic range image. So, you use this just like you would use a reglar environment map.