Just a quick note, if it may help others.  I was rendering an indoor scene with lights in the interior, and came across something that apparently is a bug in Lux.  Everything was pretty good, and then all of a sudden fireflies started growing and growing. 

They have a newer build out that seems to fix this; however it is slower to load and slower to render.  It is using precise math; which the normal build doesn't use.

Here is the link to the post that i saw that mentions this: http://www.luxrender.net/forum/viewtopic.php?f=16&t=4374

And here is the link to the newer build:  http://www.luxrender.net/forum/viewtopic.php?f=30&t=4382

It seems to be working fine for me so far; and even the lighting looks better.