Of his several choral cycles, Morten Lauridsen's Lux Aeterna (Light Eternal) has become the most often performed. The five-movement work for chorus and orchestra is organized around several Latin texts addressing the idea of light.

The first movement, "Introitus" (Entrance), text excerpted from the Requiem Mass, begins at two pitch extremes. While the basses hold a low pedal note, the violins sustain a high harmonic. Between them enter the strings, first cellos, then violas, and violins. Their motive, drawn from the second work in Lauridsen's cycle Les chansons des roses (Songs of Roses), recurs throughout the work in various incarnations. Following the introduction, the chorus enters, a cappella, closely spaced and hushed. Next a canon on "et lux perpetua" begins a swell that culminates in a majestic but piteous tutti cry on "Exaudi orationem meam" (Hear my prayer). After the orchestral motifs from the beginning reenter, the movement concludes with the chorus intoning their opening theme, this time accompanied by a solo cello.

"Introitus" flows directly into the second movement, "In te, Domine, speravi" (In You, Lord, I Have Trusted), the text of which is drawn from the "Te Deum." Suddenly the hope of the major mode has shifted to minor, and the use of chromaticism increases. In this complex movement, Lauridsen employs more complicated contrapuntal procedures such as the cantus firmus (here, the seventeenth century German hymn-tune "Herzliebster Jesu," heard in the bass trombone) and inverted canon (in the chorus at "fiat misercordia"). Lauridsen continues to contrast musical elements, juxtaposing the a cappella chorus with the orchestra, or pairing men's voices against women's.

The cellos and basses supply the downbeat only to the central movement of the cycle, the a cappella motet, "O nata lux" (O Born Light), with text from a hymn for the Divine Office. The close-voiced homophony of the chorus gives way to more independent polyphony, which reaches a peak with the quoting of a motive from Lauridsen's motet "O magnum mysterium" and then subsides into the opening texture. "O nata lux" is the movement most often excerpted from the cycle. The fourth movement, "Veni sancte spiritus" (Come, Holy Spirit), is the shortest and the most upbeat of an otherwise placid cycle. The text, drawn from the twelfth century sequence for Pentecost, has a marked rhythm which Lauridsen realizes in an exuberant triple meter; its setting employs a simple orchestral accompaniment to the spirited choral singing, appropriately at its most florid in the central stanza, which references light.

The momentum of the "Veni sancte spiritus" runs headlong into the deliberate pace of the final movement, "Agnus dei - lux aeterna" (Lamb of God - Light Eternal). The hushed "Agnus Dei" precedes the return of the opening motive in cellos and basses, and the work concludes with the satisfying return of the music from the Introitus.

A non-liturgical Requiem of sorts, Lux Aeterna became an immediate favorite for its lyrical melodies, poignant harmonies, and tonal consistency. The Los Angeles Master Chorale premiered the work in 1997; their recording won for the composer a Grammy in 1999.