Aramaic: בוצינא דקרדינותא
Hebrew: אור החושך, Light of darkness
AKA: קו המידה, “measuring line”
This is the root of Gevura at the highest level of Ketter. It was designed to restrict the Light of the Endless during the process of creating the Sefirot.
It is called the light (candle) of darkness because it defines the borders between the Light and darkness. That is why it comes from the highest level of Ketter.
Read the study of Zohar Beresheet A #1
Synonyms:
בוצינא דקרדינותא, קו במידה