"O Trinity, O Blessed Light"

Last year, I noticed a small feature in "O Trinity, O Blessed Light" (Lutheran Worship #487).*  It's sung to the tune "Steht auf, ihr lieben Kinderlein."  Here's the third phrase:

In the first verse, the text here is "The fi'ry sun is going down," and the descent in the tune mirrors this "going down."

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*In The Lutheran Service Book, this hymn appears as "O Blessed Light, O Trinity" (#890), but it's sung to a different tune, and the translation of the first verse is different.