The term “dark age” as it is used wrt European history means an age for which no physical evidence exists. The simplest possible explanation for such an age is that it simply did not happen. A number of very good scholars now believe that we are basically living more like 1700 years after Christ than like 2000 years.
The term “Dark Ages” was coined by European Protestants who were referring to the repressive, feudalistic reign of the Roman Catholic Church and the corrupt, truth-suppressing Papacy. During those Dark Ages—people neither could nor were allowed to read the Bible and hear God’s revelation directly. The Catholic hierarchy were worried about their authority being threatened.
It wasn’t until after the invention of the printing press and the Protestant Reformation that the “Light” was able to shine forth in Europe again. And don’t forget, it was the Protestant Reformation—not the “Enlightenment” that was the prime mover of scientific research and innovation as well.