There where multiple issues found in the urban scene that manifested themselves in a "night" render:
* The streetlight GDBs had corrupted source pointing (normal) vectors.
The made the sources point more in the +X direction than down (-Z).
* The INT files for the Sodium and Mercury lamps needed to be rescaled
to produce the correct luminance values.
* The source materials were updated to use the normalized shape (constant
total power vs. shape) feature.
The updates to the Urban scene were checked into the "base" trunk and 4.5.1 tag.
See bug #623 for more information.