What wealth of evidence?
I believe it was called the Dark Ages because it was dark. I believe there were numerous celestial impact events that created a dust veil over the whole earth. Probably a terrible time on earth.
As for actual physical darkness, I won't speculate. No doubt life was dim enough under the mud and thatch, but life has been "nasty, short, and brutish" for most of the planet, most of the time.
LOL....hey, who turned out the lights?
“numerous celestial impact”
Add those to our current cultural decline and we could have DAII.