John says of the Lord: 

     This is the true light which lighteneth every man (John
     1:9).

     The people that sit in darkness have seen a great light,
     and to them that were sitting in the shadow of death light
     is sprung up (Matt. 4:16).

     I will give thee for a covenant of the people, for a light
     of the Gentiles (Isa. 13:6).

     I have established Thee for a light of the Gentiles that
     Thou mayest be My salvation unto the end of the earth
     (Isa. 19:6).

     The nations of them that are saved shall walk in His light
     (Apoc. 21:24).

     Send out Thy light and Thy truth; let them lead me (Psalm
     43:3).

In these and other passages the Lord is called light from Divine truth, which is from Him; and the truth itself is likewise called light.  As light in the heavens is from the Lord as a sun, so when He was transfigured before Peter, James, and John: 

     His face did shine as the sun, and His raiment was white
     as the light (Matt. 17:2).

     And His garments became shining, exceeding white as snow,
     so as no fuller on earth can whiten them (Mark 9:3; Matt.
     17:2).

The Lord’s garments had this appearance because they represented Divine truth which is from Him in the heavens, “garments” also in the Word signifying truths,{1} consequently it is said in David: 

     O Jehovah, Thou coverest Thyself with light as with a
     garment (Psalm 104:2).

{Footnote 1} In the Word “garments” signify truths, because truths clothe good (n. 1073, 2576, 5248, 5319, 5954, 9216, 9952, 10536).  The Lord’s garments when He was transfigured signified Divine truth going forth from His Divine love (n. 9212, 9216).

130.  That light in the heavens is spiritual and that this light is Divine truth may be inferred also from the fact that men as well as angels have spiritual light, and have enlightenment from that light so far as they are in intelligence and wisdom from Divine truth.  Man’s spiritual light is the light of his understanding, and the objects of that light are truths, which he arranges analytically into groups, forms into reason, and from them draws conclusions in series.{1} The natural man does not know that the light from which the understanding sees such things is a real light, for he neither sees it with his eyes nor perceives it by thought.  And yet there are many who recognize this light, and distinguish it from the natural light in which those are who think naturally and not spiritually.  Those think naturally who take account of the world only, and attribute all things to nature; while those think spiritually who take account of heaven and attribute all things to the Divine.  It has often been granted me to perceive and also to see that there is a true light that enlightens the mind, wholly distinct from the light that is called