The Dark Ages were named in hindsight, with soft start and end dates, purposefully chosen. This period encompassed the Little Ice Age that put Europe in a long period of unusually cold and wet years included volcanic darkening events culminating in 536. That was the canonical "worst year" for humans to live. 4 years later, the Plague of Justinian wiped out tens of millions of people. It was a dark time, to say the least.