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. The Light of Christ influences people for good and prepares them to receive the Holy Ghost. One manifestation of the Light of Christ is what we call a conscience.
The Light of Christ "proceedeth forth from the presence of God to fill the immensity of space." It is "the light which is in all things, which giveth life to all things, which is the law by which all things are governed" (D&C 88:12-13; see also D&C 88:6-11). This power is an influence for good in the lives of all people (see John 1:9; D&C 93:2). In the scriptures, the Light of Christ is sometimes called the Spirit of the Lord, the Spirit of God, the Spirit of Christ, or the Light of Life.
The Light of Christ should not be confused with the Holy Ghost. It is not a personage, as the Holy Ghost is. Its influence leads people to find the true gospel, be baptized, and receive the gift of the Holy Ghost (see John 12:46; Alma 26:14-15).
Conscience is a manifestation of the Light of Christ, enabling us to judge good from evil. The prophet Mormon taught: "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. … And now, my brethren, seeing that ye know the light by which ye may judge, which light is the light of Christ, see that ye do not judge wrongfully; for with that same judgment which ye judge ye shall also be judged" (Moroni 7:16, 18).