25d39a0e_der_com___Revit_3D__March_2008__In_Revit_2009___
[Revit 2008 Feature] AccuRender environment settings, sun and sky settings [For more information] Controlling Lighting in a Rendered Image, Specifying the Background for a Rendered Image [In Revit 2009...] 
When you define render settings, you specify whether the sky is cloudy or hazy (or both), or a solid color. For the sun position, you can select from predefined settings, or define a sun position based on date/time/location or azimuth/altitude.
BIMBuilder.com / Revit 3D: March 2008
In Revit 2009...