HDRI Lighting

This tutorial covers lighting a scene using an HDRI image.  Technically any image can be used, but the term that is commonly used for this is referred to as HDRI.  Essentially, what works best is a seemingly 360 pano image.  It doesn't have to be HDR.  

So to setup the scene, first remove any lamps, unless you desire extra light on top of what will be provided by the scene.

Select the world tab, and make the following parameter changes.

Next download an 'HDRI' image that you find online.  The following one is suitable for this application.  

Next, select the camera and add a texture to it.  Apply the following settings to the new texture, loading in the HDRI image you found.

 Upon rendering the scene, you'll notice now that the entire scene is lit based on the luminance and color of the pixels as applied to a sphere around the world.

If we apply a reflective material to the ring, we now have a gold looking shiny ring, with seemingly meaningful and realistic reflections applied to it.  This works well for very realistic scenes with reflective objects.