The Bible refers to God and Christ as sources of light and enlightenment, and Satan as the source of darkness and blindness. Scriptures in addition to the Bible, especially the Doctrine and Covenants, give even more insight into the source, nature, and purpose of light.
From Doctrine and Covenants, section 88:
- 6 He that ascended up on high, as also he descended below all things, in that he comprehended all things, that he might be in all and through all things, the light of truth;
- 7 Which truth shineth. This is the light of Christ. As also he is in the sun, and the light of the sun, and the power thereof by which it was made.
- 8 As also he is in the moon, and is the light of the moon, and the power thereof by which it was made;
- 9 As also the light of the stars, and the power thereof by which they were made;
- 11 And the light which shineth, which giveth you light, is through him who enlighteneth your eyes, which is the same light that quickeneth your understandings;
- 12 Which light proceedeth forth from the presence of God to fill the immensity of space—
- 13 The light which is in all things, which giveth life to all things, which is the law by which all things are governed, even the power of God who sitteth upon his throne, who is in the bosom of eternity, who is in the midst of all things.
- 40 For intelligence cleaveth unto intelligence; wisdom receiveth wisdom; truth embraceth truth; virtue loveth virtue; light cleaveth unto light; mercy hath compassion on mercy and claimeth her own; justice continueth its course and claimeth its own; judgment goeth before the face of him who sitteth upon the throne and governeth and executeth all things.
- 44 And they give light to each other in their times and in their seasons, in their minutes, in their hours, in their days, in their weeks, in their months, in their years—all these are one year with God, but not with man.
- 45 The earth rolls upon her wings, and the sun giveth his light by day, and the moon giveth her light by night, and the stars also give their light, as they roll upon their wings in their glory, in the midst of the power of God.
- 49 The light shineth in darkness, and the darkness comprehendeth it not; nevertheless, the day shall come when you shall comprehend even God, being quickened in him and by him.
- 50 Then shall ye know that ye have seen me, that I am, and that I am the true light that is in you, and that you are in me; otherwise ye could not abound.
Thus, the revelations in the Doctrine and Covenants tell us that light powers the universe and is the law that governs it. This light emanates from God and Christ; it is intelligence, or light and truth; it can fill us, if we focus our feelings, thoughts, and actions upon the Lord. Filled with this light, men can comprehend even God; darkness cannot comprehend God.
From Doctrine and Covenants, section 93:
- 2 And that I am the true light that lighteth every man that cometh into the world;
- 9 The light and the Redeemer of the world; the Spirit of truth, who came into the world, because the world was made by him, and in him was the life of men and the light of men.
- 28 He that keepeth his commandments receiveth truth and light, until he is glorified in truth and knoweth all things.
- 29 Man was also in the beginning with God. Intelligence, or the light of truth, was not created or made, neither indeed can be.
- 31 Behold, here is the agency of man, and here is the condemnation of man; because that which was from the beginning is plainly manifest unto them, and they receive not the light.
- 32 And every man whose spirit receiveth not the light is under condemnation.
- 36 The glory of God is intelligence, or, in other words, light and truth.
- 37 Light and truth forsake that evil one.
Christ is the spirit of truth; He is the light of men. This light (intelligence) had no beginning—it has always existed. Man has agency—he can choose light or darkness. Those who keep the Lord's commandments will receive more and more light until they are glorified and know all things.
From Doctrine and Covenants, section 45:
- 7 For verily I say unto you that I am Alpha and Omega, the beginning and the end, the light and the life of the world—a light that shineth in darkness and the darkness comprehendeth it not.
- 9 And even so I have sent mine everlasting covenant into the world, to be a light to the world, and to be a standard for my people, and for the Gentiles to seek to it, and to be a messenger before my face to prepare the way before me.
- 28 And when the times of the Gentiles is come in, a light shall break forth among them that sit in darkness, and it shall be the fulness of my gospel;
- 29 But they receive it not; for they perceive not the light, and they turn their hearts from me because of the precepts of men.
The everlasting gospel has always existed, but it has been restored in its fulness in the Last Dispensation of Time as The Church of Jesus Christ of Latter-day Saints. The restored gospel has largely been rejected by men, because of the precepts of men. (See also, Doctrine and Covenants 10: 21, 58, 61-62, 70; 50: 24, 27; 84: 45-46, 54; 6: 21, 27-28; 11: 11, 19, 28; 106: 5, 8; 124: 6, 9.)
With Light comes Responsibility
A man who increases in light has more responsibility than a man who lives in ignorance. He who sins against the light is more culpable than he who sins in ignorance:
- For he will not suffer you that ye shall live in your iniquities, to destroy his people. I say unto you, Nay; he would rather suffer that the Lamanites might destroy all his people who are called the people of Nephi, if it were possible that they could fall into sins and transgressions, after having had so much light and so much knowledge given unto them of the Lord their God;
- And now behold I say unto you, that if this people, who have received so many blessings from the hand of the Lord, should transgress contrary to the light and knowledge which they do have, I say unto you that if this be the case, that if they should fall into transgression, it would be far more tolerable for the Lamanites than for them (Alma 9:19, 23). 
A man who sins against light and knowledge will lose the light that he has:
- And he that repents not, from him shall be taken even the light which he has received; for my Spirit shall not always strive with man, saith the Lord of Hosts (Doctrine and Covenants 1:33).
Angels of Light
Heavenly messengers have a brilliance that is almost intolerable to men, and almost always initially frightening. Joseph Smith's account is recorded in the Pearl of Great Price, Joseph Smith History 1:16, 17:
- I saw a pillar of light exactly over my head, above the brightness of the sun, which descended gradually until it fell upon me.
- It no sooner appeared than I found myself delivered from the enemy which held me bound. When the light rested upon me I saw two Personages, whose brightness and glory defy all description, standing above me in the air. One of them spake unto me, calling me by name and said, pointing to the other—This is My Beloved Son. Hear Him!
- While I was thus in the act of calling upon God, I discovered a light appearing in my room, which continued to increase until the room was lighter than at noonday, when immediately a personage appeared at my bedside, standing in the air, for his feet did not touch the floor.
- Not only was his robe exceedingly white, but his whole person was glorious beyond description, and his countenance truly like lightning. The room was exceedingly light, but not so very bright as immediately around his person. When I first looked upon him, I was afraid; but the fear soon left me (Joseph Smith History 1:30, 32).
Satan can appear as an angel of light in order to deceive men. However, he cannot appear as glorious as an angel sent from the realms of heaven. Thus, the power of discernment is needed to keep from being deceived:
- And our spirits must have become like unto him, and we become devils, angels to a devil, to be shut out from the presence of our God, and to remain with the father of lies, in misery, like unto himself; yea, to that being who beguiled our first parents, who transformeth himself nigh unto an angel of light, and stirreth up the children of men unto secret combinations of murder and all manner of secret works of darkness (2 Nephi 9:9).
- And no marvel; for Satan himself is transformed into an angel of light (2 Corinthians 11: 14).
- And it came to pass that when Moses had said these words, behold, Satan came tempting him, saying: Moses, son of man, worship me.
- And it came to pass that Moses looked upon Satan and said: Who art thou? For behold, I am a son of God, in the similitude of his Only Begotten; and where is thy glory, that I should worship thee?
- For behold, I could not look upon God, except his glory should come upon me, and I were transfigured before him. But I can look upon thee in the natural man. Is it not so, surely?
- Blessed be the name of my God, for his Spirit hath not altogether withdrawn from me, or else where is thy glory, for it is darkness unto me? And I can judge between thee and God; for God said unto me: Worship God, for him only shalt thou serve (Pearl of Great Price, Moses 1:12-15).
- The Lamanites sinned because of the traditions of their fathers. They were ignorant of the commandments of God.