The edition of the third motet of the cycle is also based on Librone 1 (ff. 164v–165r), where it was written by Scribe A, like all motets of this cycle.
The only mistake made by the scribe was the wrongly positioned ‘et’ in the expression ‘rex et sponsus’ (C writes ‘et rex sponsus’) and the wrong spelling of lumen as ‘lumem’ (in A). Again the spelling of ‘Yhesus’ is divergent from the more classical Jesus or Iesus.
The source text is the same Christological prayer Ave Domine Iesu Christe verbum patris, and so is the topic of the motet, clearly focused on devotion to Christ. The mention of ‘lumen’ right at the opening of the motet could be a reference to the liturgical text this motet was sung to, namely, according to the rubric ‘loco Patrem’, the Credo. There as well Christ is referred to as ‘lumen de lumine’.^[1]

^[1] Eva Ferro, ‘“Old Texts for New Music”? Textual and Philological Observations on the Cycles “Salve Mater Salvatoris” and “Ave Domine Iesu Christe” from Librone 1’, in Motet Cycles between Devotion and Liturgy, ed. Daniele V. Filippi and Agnese Pavanello, Schola Cantorum Basiliensis Scripta, 7 (Basel: Schwabe, 2019), 189–218.