When you look at Orthodox icons one of the things that strikes you is how flat they look. Again, this flatness might be mistaken for artistic primitiveness or inexpertness. This assumption would be mistaken. Like all things in icons this perception of flatness has a theological aspect.

Orthodox icons appear flat because iconographers are working with theological assumptions regarding the Divine Light, the Uncreated Light in Heaven. Recall, icons are depictions of persons alive in heaven. It is entirely acceptable to approach icons as "Windows into Heaven." If so, how are we to depict Heaven?

One aspect of this depiction is to take a cue from Revelation 21

Then I saw a new heaven and a new earth, for the first heaven and the first earth had passed away, and there was no longer any sea. I saw the Holy City, the new Jerusalem, coming down out of heaven from God, prepared as a bride beautifully dressed for her husband. And I heard a loud voice from the throne saying, "Now the dwelling of God is with men, and he will live with them. They will be his people, and God himself will be with them and be their God. He will wipe every tear from their eyes. There will be no more death or mourning or crying or pain, for the old order of things has passed away."

...I did not see a temple in the city, because the Lord God Almighty and the Lamb are its temple. The city does not need the sun or the moon to shine on it, for the glory of God gives it light, and the Lamb is its lamp. The nations will walk by its light, and the kings of the earth will bring their splendor into it. On no day will its gates ever be shut, for there will be no night there.

Icons attempt to represent this Uncreated Light through three things, all of which contribute to that sense of flatness.

First, icons tend not to show backgrounds. Instead, icon backgrounds tend to be filled with a diffuse golden light. This lack of a formal background contributes to the sense of a lack of depth, but we can now appreciate its theological aspect: A depiction of a land filled with light.

Second, icons don't show shadows. For two reasons. First, shadows, archetypally, imply darkness and even evil. Second, shadows are cast by the localized light of the sun (the Created Light). In Heaven the Uncreated Light is not localized, it is omnipresent. Thus, there are no shadows in Heaven.

Finally, related to the point about shadows, iconographers use little or no chiaroscuro. Chiaroscuro is the contrast between light and dark in painting. It can be used to make pictures very dramatic. It also makes the picture rich and deep, perspectively speaking. Icons don't use chiaroscuro for the reasons we have just observed. In Heaven, infused with the omnipresent Divine Light, there are no striking light/dark contrasts.

All in all, icons appear "flat" for all these related theological reasons. But with this theological understanding in place we are in a much better situation to appreciate the rich theology of the icon.