I will be gracious to whom I will be gracious, and I will have compassion on whom I will have compassion. So it shall be, while My glory passes by, that I will put you in the cleft of the rock, and will cover you with My hand while I pass by. The whole point about God being Light is that the splendor and radiance of His immediate presence is so intense it must be veiled in clouds of thick darkness. Otherwise mere mortals would be burned to a crisp if they came into the unveiled presence of His effulgent power. Spiritual realities are more permanent and more substantial that the shadows they cast into our physical world.
Light is a common symbol in the Bible for truth as opposed to ignorance and error.
He who follows Me shall not walk in darkness, but have the light of life. The New Testament furthermore insists that the man Christ Jesus is the exact visible expression of God the invisible. God, were his Light unveiled, would fill and flood the entire universe with His presence to such a degree that there could be no ordinary night time anywhere. Living as we do at present in a world still relatively dark, we await the coming of the Dawn. In current thinking on the nature of the vacuum, space has a granular structure and is composed of particles emerging from and vanishing back into the background sea of Zero Point Energy.