The light of Christ is the divine energy, power, or influence that proceeds from God through Christ and gives life and light to all things. In John 8:12 it says,
Every person is born with the light of Christ within him or her. The light of Christ serves as the person’s conscience and natural moral guide. At times, the Holy Ghost may also testify to a person and lead him or her along the gospel path, until he or she may gain the constant presence of the Holy Ghost after baptism by the proper authority. The light of Christ can lead a person toward salvation.
But he that doeth truth cometh to the light, that his deeds may be made manifest, that they are wrought in God.(John 3:21)
The light of Christ dims within a person, if that person’s body becomes an unclean place for it to dwell, or if the person constantly makes choices that lead him away from the light and toward the darkness of evil.
The canon of The Church of Jesus Christ of Latter-day Saints, sometimes nicknamed the “Mormon Church,” has all the biblical references regarding the light of Christ, plus additional knowledge provided by other ancient texts and records of modern revelation.
The Light of Christ is the Law and the Power by which all things are governed on heaven and earth:
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 lightof truth; 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.
As also he is in the moon, and is the light of the moon, and the power thereof by which it was made; As also the light of the stars, and the power thereof by which they were made; And the earth also, and the power thereof, even the earth upon which you stand. 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; Which light proceedeth forth from the presence of God to fill the immensity of space—
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 (Doctrine and Covenants 88:6-13).
The Light of Christ is not the Holy Ghost, but it enlightens all of God’s children.
For the word of the Lord is truth, and whatsoever is truth is light, and whatsoever is light is Spirit, even the Spirit of Jesus Christ. And the Spirit giveth light to every man that cometh into the world; and the Spirit enlighteneth every man through the world, that hearkeneth to the voice of the Spirit. And every one that hearkeneth to the voice of the Spirit cometh unto God, even the Father (Doctrine and Covenants 84:45-47).
For behold, the Spirit of Christ is given to every man, that he may know good from evil; wherefore, I show unto you the way to judge; for every thing which inviteth to do good, and to persuade to believe in Christ, is sent forth by the power and gift of Christ; wherefore ye may know with a perfect knowledge it is of God.
But behold, that which is of God inviteth and enticeth to do good continually; wherefore, every thing which inviteth and enticeth to do good, and to love God, and to serve him, is inspired of God (Book of Mormon, Moroni 7:16, 13).
Christ is the Light of the World:
…there is no other way or means whereby man can be saved, only in and through Christ. Behold, he is the life and the light of the world. Behold, he is the word of truth and righteousness (BofM, 38:9).
I am the light and the life of the world. I am Alpha and Omega, the beginning and the end (BofM, 3 Nephi 9:18).
That which is of God is light; and he that receiveth light, and continueth in God, receiveth more light; and that light groweth brighter and brighter until the perfect day (D&C 50:24).
Losing the Light of Christ
The Light of Christ is the source of our conscience, and our conscience helps us discern between right and wrong, good and evil. It used to be in American society, that Judeo-Christian ethics provided a moral context mostly in line with God’s commandments for His children. Stealing and inappropriate sexual activity could arouse a great deal of guilt in youth, and society supported the norms that caused that guilt. Nowadays, any sort of moral context is dissipating. Thomas S. Monson, Prophet and President of the Church of Jesus Christ, at the October 2011 General Conference of the Church, quoted a study of young people completed in 2008 with 230 young adults from across America participating:
“The interviewers asked open-ended questions about right and wrong, moral dilemmas and the meaning of life. In the rambling answers, …you see the young people groping to say anything sensible on these matters. But they just don’t have the categories or vocabulary to do so.
“When asked to describe a moral dilemma, they had faced, two-thirds of the young people either couldn’t answer the question or described problems that are not moral at all, like whether they could afford to rent a certain apartment or whether they had enough quarters to feed the meter at a parking spot.
“The default position, which most of them came back to again and again, is that moral choices are just a matter of individual taste. Rejecting blind deference to authority, many of the young people have gone off to the other extreme” — simply following their feelings and desires, with no moral context.
The interviewers concluded that these young people “had not been given the resources—by schools, institutions, or families—to cultivate their moral intuitions” (David Brooks, “If it Feels Right…,” New York Times, Sep. 12, 2011, nytimes.com.)
The Spirit of God will not always contend with man.
For the Spirit of the Lord will not always strive with man. And when the Spirit ceaseth to strive with man then cometh speedy destruction, and this grieveth my soul.
And again, the Lord God hath commanded that men should not murder; that they should not lie; that they should not steal; that they should not take the name of the Lord their God in vain; that they should not envy; that they should not have malice; that they should not contend one with another; that they should not commit whoredoms; and that they should do none of these things; for whoso doeth them shall perish.
For none of these iniquities come of the Lord; for he doeth that which is good among the children of men; and he doeth nothing save it be plain unto the children of men; and he inviteth them all to come unto him and partake of his goodness; and he denieth none that come unto him, black and white, bond and free, male and female; and he remembereth the heathen; and all are alike unto God, both Jew and Gentile (BofM, 2 Nephi 26:11, 32, 33).
The Light of Christ will penetrate the darkness to find any soul who desires to repent. Said Mormon apostle Jeffrey R. Holland:
I do not know who in this vast audience today may need to hear the message of forgiveness inherent in this parable, but however late you think you are, however many chances you think you have missed, however many mistakes you feel you have made or talents you think you don’t have, or however far from home and family and God you feel you have traveled, I testify that you have not traveled beyond the reach of divine love. It is not possible for you to sink lower than the infinite light of Christ’s Atonement shines. 
Said Mormon apostle Robert D. Hales:
You may already know, deep in your soul, that God lives. You may not know all about Him yet and do not understand all His ways, but the light of belief is within you, waiting to be awakened and intensified by the Spirit of God and the Light of Christ, which you are born with. 
Said Mormon apostle Henry B. Eyring:
Every child of Heavenly Father born in the world is given at birth, as a free gift, the Light of Christ. You have felt that. It is the sense of what is right and what is wrong and what is true and what is false. That has been with you since your journey in life began.