This Psalm focuses on this world as God originally created it before it was affected by sin. This chapter parallels Genesis chapter 1. It is as if the author had a copy of Genesis 1 in front of him and God inspired him to write a commentary on it.
 Bless the LORD, O my soul. O LORD my God, Thou art very great; Thou art clothed with honour and majesty.
The last part of this verse states that God is very great. The ideas is about appreciating who God is and appreciating this world as He created it. The writer focuses on how God created this world before it was corrupted by sin. Perhaps this aspect is emphasized because when Jesus returns, He will restore this world the way God intended it to be before the influence of sin corrupted it.
The last phrase of verse 1 states, "Thou art clothed with honour (splendor) and majesty.” This is about appreciating our world and it is poetically describing God as being wonderful. The idea in effect is that if we love God, we think of Him as being special. We are simply to praise Him for how wonderful this world was as originally intended by God.
 Who coverest Thyself with light as with a garment: who stretchest out the heavens like a curtain:
Genesis 1 first mentions the concept of light in verse 3 although the sun was not created until the fourth day of creation in Genesis 1:16. Therefore, the “light” in this verse in Psalm 104 and also in Genesis 1:3 does not refer to any created light like the sun or any of the stars.
So what does “God is light” mean? It is to teach us that we can understand aspects of Him and in effect a spotlight is put on Him so we can comprehend aspects of His existence.
Next the verse says God stretches out the heavens like a curtain. Scientists will explain that the universe as we know it is expanding. What our universe is expanding into is beyond my ability to grasp. From the point of the writer's knowledge of creation, I believe he is commenting on Genesis 1:1 that says God created the heavens and the earth. All praise to the One who created and sustains this world by His word.