What are the "Dark Ages"?
Medievalists avoid this term. Dark? You mean the sun didn't come up? Until the late nineteenth century, with the development of electricity (which did not reach all parts of even the western world until the middle of the twentieth century), everything was lit only by fire.
Or dark? As in horrible things happened? Well, modern people have the technology to do even more horrible things faster and on a wider scale. Unfortunately humans tend to do horrible things to each other a lot, though everyone (including me) keeps hoping we'll stop soon.
The term Dark Ages was originally a specifically British term, meaning the late fifth and sixth century, after the collapse of Roman Britain, before the Anglo-Saxons who had settled in Britain (or, as they called it, England) became Christianized and started writing things down. Originally the sixth century was considered "dark" because we knew so little about it. We know a lot more about what was going on in continental Europe.
Because so little was known about the so-called Dark Ages in Britain, it was a great time to set the much later epics and romances about (for example) King Arthur.
But "dark" always has a pejorative context, implying more than just something unknown (ask anyone with a lot of melanin in their skin). So medievalists don't use the term. (The "Light Ages"? Well, probably not.)
Above is an image of a sarcophagus from late antiquity, the period often called the Dark Ages. It doesn't look so crude and rude to me.
Click here for more on the "fall" of the Roman Empire.