I am a student at the University of Southern Mississippi and we have been experimenting with the C4 game engine for quite a while in our Arch. & Construction Visualization master's degree program. It is relatively inexpensive to buy a commercial license and is redistributable once you own a license. In addition they also release to you the source code (which is C++ i believe) to which you can modify as needed. We have used it to create a real time lighting study and are currently experimenting with real time visualizations as well. Another key note about the C4 engine is that the license is ongoing and never expires, and includes ALL future updates and versions as long as you own the license. It also doesnt require a super computer to run, like the crysis engine which is really heavy on the graphics requirements..
http://www.terathon.com/ - C4 Game Engine
http://www.engr.psu.edu/convr/procee...mission_20.pdf - example of one of the studies conducted by our department advisor and a collegue of mine... using the C4 engine
there is also an arch/vis company in texas doing that does alot of work using Unreal Engine 3... HKSVIZ used UT3 engine for the Dallas Cowboys stadium...
http://www.businessweek.com/innovate...221_129534.htm
http://www.hksinc.com/
~Shane G.