SBT.. it's not a light at all.. it's actual name is "Environment Sphere" and comes in the base D|S props.  I haven't noticed much at all as far as shadows go as the light source is literally everywhere.. but with the sunlight preset and keeping the gain at about 6 it does give some nice subtle lighting.. and I've noticed that if I put a diffuse texture on it the lighting takes on the tones of the picture quite nicely.

If you're planning on using it.. you'll notice some things.  on the surfaces tab.. the diffuse is disabled by default.. you have to enable it(of course).  then on the parameters tab.. nothing will show unless you select the "show hidden properties" option.. then everything is locked and you have to manually unlock for any adjustments you want to make.