This page provides Scriptural references that demonstrate that God is light.
This then is the message which we have heard of him, and declare unto you, that God is light, and in him is no darkness at all."
Epistle of I John, Chapter 1, verse 5
The LORD is my light and my salvation; whom shall I fear? the LORD is the strength of my life; of whom shall I be afraid? Psalms 27:1
For with thee is the fountain of life: in thy light shall we see light. Psalms 36:9
For the LORD God is a sun and shield: the LORD will give grace and glory: no good thing will he withhold from them that walk uprightly. Psalms 84:11
The sun shall be no more thy light by day; neither for brightness shall the moon give light unto thee: but the LORD shall be unto thee an everlasting light, and thy God thy glory. Isaiah 60:19
In him was life; and the life was the light of men.John 1:4
That was the true Light, which lighteth every man that cometh into the world. John 1:9
Then spake Jesus again unto them, saying, I am the light of the world: he that followeth me shall not walk in darkness, but shall have the light of life. John 8:12
As long as I am in the world, I am the light of the world. John 9:5
Then Jesus said unto them, Yet a little while is the light with you. Walk while ye have the light, lest darkness come upon you: for he that walketh in darkness knoweth not whither he goeth. John 12:35
While ye have light, believe in the light, that ye may be the children of light. These things spake Jesus, and departed, and did hide himself from them. John 12:36
Who only hath immortality, dwelling in the light which no man can approach unto; whom no man hath seen, nor can see: to whom be honour and power everlasting. Amen. 1 Timothy 6:16
Every good gift and every perfect gift is from above, and cometh down from the Father of lights, with whom is no variableness, neither shadow of turning. James 1:17
And the city had no need of the sun, neither of the moon, to shine in it: for the glory of God did lighten it, and the Lamb is the light thereof. Revelation 21:23
And there shall be no night there; and they need no candle, neither light of the sun; for the Lord God giveth them light: and they shall reign for ever and ever. Revelation 22:5
That He is light is illustrative of many truths about God. First of all He is to be known as opposed to hidden in darkness. God is not hiding, He is shining forth to all who will choose to see Him. Light reveals the truth of a situation because it allows one to see what is there.
Secondly, that God is light illustrates that He is not darkness. You cannot have light and darkness in the same place - they cannot, by definition, exist together. Although light can dispel darkness, darkness cannot dispel light.