The Doctrine and Covenants and Angel of Light 

Up until at least 1953, the Mormon Church First Presidency published an official statement as an Explanatory Introduction to the The Doctrine and Covenants, one of the Church's Standard Works of Scripture. The Pearl of Great Price, is a compilation of revelations which Joseph Smith (and a few other Mormon prophets) said they received from God.

The Explanatory Introduction states that Joseph Smith was shown, by an angel named Moroni, gold plates of ancient origin. These plates, when translated by Joseph Smith "through the gift and power of God," were published as the Book of Mormon.

The Explanatory Introduction states very specifically that the angel, Moroni, was an angel of light. Here is the quotation:

 "...In September, 1823, and at later times, Joseph Smith received visitations from Moroni, an angel of light,who revealed the resting place of the ancient record from which The Book of Mormon was afterward translated."
See a photocopy of the actual page from the Doctrine and Covenants.

Why would the Mormon First Presidency use this term "angel of light"?
Did they know what they were saying? They must have because Mormon Apostle Bruce R. McConkie certainly did. McConkie wrote the widely read book, Mormon Doctrine, which has been printed by Bookcraft Press in Salt Lake City since the 1950's. In that book McConkie references the term "Angel of Light" with two words-SEE DEVIL!