1 O lux beata Trinitas,
et principalis unitas,
jam sol recedit igneus,
infundo lumen cordibus.
2 Te mane laudum carmine,
Te deprecemur vespere,
Te nostra suplex gloria
per cuncta laudet cesula.
3 Deo patri sit gloria,
ejusque soli filio
cum spiritu paracleto
nunc et per omne seculum.
Source: Evangelisch-Lutherisches Gesang-Buch: worin die gebräuchlichsten alten Kirchen-Lieder Dr. M.Lutheri und anderer reinen lehrer und zeugen Gottes, zur Befoederung der wahren ... (2. verm. Aus.) #189
O Lux beata Trinitas, Et principalis Unitas. St. Ambrose. [Evening.] This is one of the twelve hymns which the Benedictine editors regarded as undoubtedly the work of St. Ambrose. It is cited as by St. Ambrose by Hinemar of Rheims in his treatise De unâ et non trinâ Deitate, 857. The original. consists of two sts. (ii. "Te mane laudum carmine") and a doxology. Its almost universal use was at Vespers on Saturday, as in the older Roman (Venice, 1478); Paris, 1643; Sarum, York, and Aberdeen Breviaries. It was sometimes also assigned to Vespers or Lauds on Trinity Sunday. Daniel, i.. No. 26, gives the original, along with the revised text of the Roman Breviary of 1632, where it begins Jam sol recedit igneu. In his notes Daniel gives the additional stanza translation in J. D. Chambers's Lauda Syon, 1857(see below); (iii. "Jam noctis tempus advenit"; iv. "Tu Christe solve vincula"; v. "Oramus ut exaudias"), which are found only in the Mozarabic Breviary, where the hymn is given for Vespers on the 2nd Sunday after the Epiphany, and at other seasons. In his further notes at iv. pp. 47-48, Daniel refers to the original text as in a 10th century Rheinau manuscript; gives the statements of Hinemar; and also cites a passage from the 21st Epistle of St. Ambrose, which he thinks clearly refers to this hymn, and so decisively settles its authorship. [Rev.W. A. Shoults, B.D.]
Mone, i. p. 372, cites this hymn as in an 8th century manuscript at Darmstadt, where it is assigned to daily Vespers. Dreves gives it in his Hymnarius Moissiacensis, 1888, from a 10th century manuscript. It is also in three manuscripts of the 11th century in the British Museum (Vesp. D. xii. f. 2 6; Harl. 2961 f. 218; Add. 30848 [a Mozarabic Breviary] f. 66 &). In the Latin Hymns of the Anglo-Saxon Church (Surtees Society), 1851, p. 1., it is printed from an 11th century manuscript at Durham (B. iii. 32, f. 2). Also in an 11th century manuscript at Corpus Christi, Cambridge (391, page 227); in the St. Gall manuscript, No. 387, of the 11th century in Migne's Patrol, xvi., col. 1407, and lxxxvi., cols. 220, 232, 699, 924; in Wackernagel, i. No. 60; in Card. Newman's Hymni Ecclesiae, 1838 and 1865, and others.
The original text has been frequently translation into German, and through three of these versions has passed into English.
i. Der du bist drei in Einigkeit. This is a full and faithful version by M. Luther, written in 1543, and first published in Klug's Gesang-Buch, Wittenberg, 1544. Thence in Wackernagel, iii. p. 29; in Schircks's edition of Luther's Geistlishe Lieder, 1854, p. 42; and the Unverfälschter Liedersegen, 1851, No. 186. Translated as:—
Thou Who art Three in Unity, True God. By K. Massie, in his Martin Luther's Spiritual Songs, 1854, p. 25. Repeated in the Ohio Lutheran Hymnal 1880, and by Dr. Bacon, 1884, p. 71.
Other translations are:—
(1) "Since Thou, the living God, art Three," by Miss Fry, 1845, p. 139. (2) “The true One God, in Persons Three," by J. Anderson, 1846, p. 23 (1847, p. 45). (3) “Thou Three in One, and One in Three," by Dr. J. Hunt, 1853, p. 53. (4) "Thou only God, the Three in One," by Dr. H. Mills, 1856, p. 223. (5) "Thou Who'rt One, and yet as Three," by Miss Manington, 1863, p. 155. (6) "Thou, Lord, art Three in Unity," by S. Garratt, in his Hymns and Translations, 1867, p. 39. (7) "Thou, Who art Three in Unity, A," by Dr. G. Macdonald, in the Sunday Magazine, 1867, p. 388, and his Exotics, 1876, p. 61.
ii. O selges licht, Dreifaltigkeit. A full and good translation by Bunsen for his Versuch, 1833, No. 41. Repeated in the Kirchen Gesang-Buchof the Eisenach Conference, 1854, No. 74. Translation as "O Trinity of blessed Light, Thou Unity," by H. J. Buckoll, 1842, p. 62.
iii. 0 werthes Licht der Christenheit. A full and good translation by M. A. von Löwenstern. It seems to have appeared in the 2nd edition, circa 1646, of the Breslau Kirchen- und Haus-Music. Mutzell, 1858, No. 288, quotes it (as No. 26 of Löwenstern's Apelles-Lieder) from the 5th edition, circa 1668. Included in Burg's Gesang-Buch, Breslau, 1746, No. 64. Translation as, "0 Holy fount of light on high," in full as No. 178 in Dr. Pagenstecher's Collection, 1864, signed, "F. C. C." [Rev. James Mearns, M.A.]
Both forms of the Latin text have been translation into English.
These forms have been translated thus:—
i. 0 Lux beata Trinita.
1. Bright and blessed Three in One. By W. L. Alexander, in his Augustine Hymn Book, 1st edition, 1849, No. 195, and again in later editions.
2. 0 Trinity of blessed light. By J. M. Neale, in the Hymnal Noted, 1852, No. 1. It is given in several collections, including Hymns Ancient & Modern, 1861 and 1875, with slight alterations ; the Hymnary, 1872, with other changes; and other hymn-books.
3. 0 Light thrice blessed, Holy Trine. By W. J. Blew, in his Church Hymn & Tune Book, 1852-55, and again in Rice's Selection from the same, 1870.
4. 0 Light! Thou  Trinity most blest. By J. D. Chambers. This is a translation of the 5th stanza and doxology form of the hymn as given in the Mozarabic Breviary (see above). It was published in Chambers's Psalter, 1852, p. 325; and his Lauda Syon, 1857, p. 56, and is No. 410 in the People's Hymnal, 1867.
Other translations are:—
1. 0 blessed lighte, 0 Trinitie, 0 Unity that is the chief. Primer, 1604.
2. 0 blessed light, 0 Trinity, 0 Unity most principal. Primer, 1615.
3. Thou ever-blessed Triune light. Hymnarium Anglicanum, 1844.
4. 0 Trinity, blest Light. I.Williams, in his Thoughts in Past Years, 1848.
5. When sinks in night that radiant sun. H. M. Macgill. 1876.
ii. Jam sol recedit igneus . This revised version of the hymn appeared in the Roman Breviary in 1632. It is the hymn on Saturdays at Vespers from the Octave of the Epiphany to Lent; also at first and second Vespers of Trinity Sunday; and also on Saturdays at Vespers from the Octave of Corpus Christi until Advent. It is translated as:—
1. Now sinks in night the flaming sun. By Bishop R. Mant. This paraphrase rather than translation appeared in his Ancient Hymns from the Roman Breviary, &c, 1837, p. 16, in 3 stanzas of 8 lines (edition 1871, p. 31). The first stanza may be said to be the translation of the Latin and the rest an expansion of the same line of thought, thus making the paiaphrase. It is in several modern collections, including Kennedy, 1863; Thring's Collection, 1882, &c; and altered as "Father of lights, Who dwell'st in light," in the 1874 Supplement to the New Congregational Hymnal; and as "The flaming sun has sunk in night," in the Hymnary, 1872.
2. Now doth the fiery sun decline. By E. Caswall, in his Lyra Catholica, 1849, pp. 36 and 108, and again in his Hymns and Poems, 1873, pp. 21 and 61. It is in several modern collections.
Other translations are:—
1. Now doth the fiery sun retire. Primer, 1685.
2. The fiery sun now rolls away. And hastens. Primer, 1706.
3. The fiery sun now rolls away. Blest Three and One, &c. Evening Office. 1710.
4. Already the bright sun departs. A. J. B. Hope.
5. Behold the fiery sun recede. F. C. Husenbeth. 1840.
6. The fiery sun is gone. W. J. Copeland. 1848.
7. The fiery sun now fades from sight. W. J. Copeland. 2nd translation 1848.
8. Behold the radiant sun departs. R. Campbell. 1850.
9. The red sun is gone. Card. Newman. 1853.
10. While fades the glowing sun away. T. J. Potter.
11. Blest Light, eternal Trinity. J. D. Aylward. This translation is followed by 5 additional stanzas.
12. The fiery sun recedes from sight. J. Wallace. 1874.
Of these translations not in common use Nos. 1, 2, 3, 5, 8, 10, and 11, are in O. Shipley's Annus Sanctus (and its Appendix), 1884.
--Excerpts from John Julian, Dictionary of Hymnology (1907)