(gradually) getting light; turning into dawn (said of the night), only in phrase ratyā vivasane at the end of night, combined in stock phrase with suriy’ uggamanaṃ pati “towards sunrise” (evidently an old phrase) at Thag.517; Ja.iv.241; Ja.v.381, Ja.v.461; Ja.vi.491; Pv.iii.8#2. Also at Snp.710.

vi + vas (uṣ) to shine, cp. vibhāti