There are two ways to translate the word "Dayspring" in verse 78. It is anatole in Greek, meaning "rising up," and Greek speakers usually use it of the sun and stars rising. It often has the sense of "from the east," since the sun rises in the east.
Its second meaning, though, is "shoot" or "branch"! It is the same word that the Septuagint, the Old Testament in Greek, uses in Jeremiah 23:5 and Zechariah 3:8; 6:12 for "Branch"! At the very least, this is a double entendre, a play on both meanings of the word, to describe the Messiah. This could be translated "the Branch from on High," which is very similar to Isaiah 4:2, "the Branch of the Lord [YHWH]."
The translators chose to use "Dayspring" because verse 79 contains the imagery of giving light in darkness, just as the dawn chases away the darkness of night. They are undoubtedly correct in their choice, but the idea of "the Branch" is lurking just behind.
Richard T. Ritenbaugh