SRF uses the phrase “Dark Ages”, referring to the period of time described by Swami Sri Yukteswar as falling in “Kali Yuga”, the less advanced period of his theory of the Yuga cycle.

Since the Renaissance, it had become common to refer to the period of time from the fall of Rome to the beginning of the Renaissance in Europe as the “Dark Ages” as well. The European concept of a “Dark Age” originated in the 1330s with the Italian scholar Petrarch, who regarded the post-Roman centuries as “dark” compared to the “light” of classical Greece and Rome.  In the late 1900’s, the term “Dark Ages” began to be replaced by the “Middle Ages”, as blanket statements describing an entire period of time as either Dark or Light began to be abandoned.

Viewing the Middle Ages as wholly dark ignores the cultural and technological developments of that time period, and ignores progress and culture in other parts of the world.

Further Reading / Watching:

https://en.wikipedia.org/wiki/Dark_Ages_(historiography)

https://shop.thegreatcourses.com/the-middle-ages-around-the-world