That Black Light demo - anyone know how it works?

Blitz3D Forums/Blitz3D Programming/That Black Light demo - anyone know how it works?

The forum is locked. These are the original blitzbasic.com forums, kept so they can still be read. No new topics, replies or edits can be made here. To join in, head over to the Blitz3D+ forums.

As the title really, all the forum links to the demo zip are gone, and I can't seem to figure out how these negative lights and fog give that visual effect.