That "sons of darkness / sons of light" thing is not really "Q-related lingo" at all, except that everyone is probably drawing on the same source.
you are correct, it was an expression used in the Dead Sea Scrolls. It's also used in the Didache, one of the earliest non-biblical text; several translations of the Didache available here:
http://www.earlychristianwritings.com/didache.html
It seems to be a common expression from the 150 BC - 150 AD time period.
Note that there is some echo of that phrase in St. Augustine. He contrasts the City of God vs. City of Man. Text of his book "City of God" here (warning, it's loooong):
https://www.newadvent.org/fathers/1201.htm
Note that St. Augustine lived about the middle of the 300s to a few decades into the 400s.
Between the Didache and St. Augustine, both incredibly influential texts, that type of contrast-language is fairly common with Christians.