"in the midst of that darkness enveloped in invisible light"

 . . . the Pharisees, sons of darkness, were awake an entire night;
the dark ones kept vigil to conceal the incomprehensible Light.
Keep vigil as bright ones on this bright night;
for even if its color is black, still it is splendid in its power.
One who splendidly watches and prays in the darkness
is wrapped in hidden brilliance in the midst of this visible darkness.

     St. Ephraem the Syrian, Hymns on the nativity I.71-74, trans. McVey, Classics of western spirituality (1989), 72 =SC 459 =CSCO 186, 9.  Headline from the German translation ("inmitten jener Finsternis | in unsichtbares Licht gehüllt") in Peter Bruns, "Im Dienste der Engel:  die Nachtwachen im syrischen Mönchtum," Römische Quartalschrift für christliche Altertumskunde und Kirchengeschichte 111, nos. 1–2 (2016): 45 (38–49).