The 1953 RLDS edition reads “upon them” rather than the correct “unto them”. Elsewhere in the text, we always get “light (un)to X”, never “light upon X” (where X refers to people). There are five other occurrences of “light unto X”, including one more that quotes the Lord:
These occurrences of “light unto X” recall the language of Isaiah:
Although the preposition in the Isaiah quote is to, the unto used elsewhere in the Book of Mormon for this expression is semantically equivalent, unlike upon.
Summary: Maintain the original preposition unto in 2 Nephi 10:14 (“I will be a light unto them forever”).