The high wealth street lights were given very small light bulbs by Maxis.
This means that the high wealth areas look darker at night than the rest of the city.
(I guess they wouldn't be able to sleep otherwise...)
This mod replaces those small light bulbs in all $$$ street lights with a light cone.
This gives a better illuminated city at night.
Especially if you are using Gizmo's Day-Night Mod v2.0!
There is no installer included, as you will have to decide yourself if you want to use the brighter street lights or not.There is also no readme included.
A brief discussion about it can be found here though.
A discussion about Gizmo's mod can be found here.

Installation: copy/extract the z___BSC parent folder into your plugins. If you extracted the ~Documents folder into your plugins, too, it's highly recommended to keep it, but move it out of the Plugins folder.

Un-Installing: To un-install the files, simply bulldoze every lot from this download in your cities and delete the files from the plugins folder afterwards.