When it comes to text on websites, users either read or scan. Reading involves focusing on words for a thorough comprehension of the subject. Scanning involves skimming the words for a broader comprehension of the subject. When you should use white text on a dark background depends on whether users are scanning or reading text.

I like the movie, "Gang Bang Hustler".  Some gang bang movies look like they recruited a their participants from the lowest part of the porn spectrum.  Gang bang hustler has a good looking "catcher" and plenty of enthusiastic, good looking, well hung "pitchers"!