mr Area Spot Light with the Lume Glow skydome

This shows the essential setup combining a soft ray shadow from a mr Area spot light with the lume glow skydome. This is from Jeff Patton.

Our only light is a regular directional light with ray shadows ... the renderer is mental ray with FG.

Select the light and convert to mr Area spot light [not a mr Area directional light ...

Move closer ... get softer ...

or, set the size larger ... get softer ...

The skydome material ...

By raising or lowering the BRIGHTNESS you can control the light of the entire scene, like a skylight.