How should we like it were stars to burn
With a passion for us we could not return?
If equal affection cannot be,
Let the more loving one be me.
--The More Loving One, W.H. Auden
Someone made an excellent point in class: light works by participation. Once you see the light, you are one with the light, even if you are in the darkness. Because your eyes have seen the light. Light cannot be seen without entering into you a little bit. You have to become familiar with the light, because it gets into your cones and rods and corneas and makes itself known there.
Even if your whole life if you sit in darkness, you are still in the light. You have still experienced a bit of the light inside of yourself. Or, rather, the light is in you. It is in your eyes, it's vision still bounces around in your memory. You cannot erase the memory of the light. It will always be there. Perhaps hidden away in some deep memory you never excavate. But it is there.
Once there is light, darkness is not quite complete. There is a little wedge of darkness that is no longer darkness, but light. Darkness has lost its comprehensive character, and just becomes a shadow. Shadows are darkness that exist because of light. Even the shadows--the darkness of the shadows--becomes partakers in the light.
Once there is light, there is nothing more than light.