Darkness is not the absence or lack of light. The reason why we can see darkness is because of the ambient light around it. Darkness is just a biological reaction to lower visible light levels and doesn't exist outside of the brain. Only the physical conditions that our brain uses to create darkness exist outside ourselves.

"But what if I am in a room where there is absolutely no light. And by light, I mean photons that wavelengths in the visible spectrum of electromagnetic radiation."

Well, that's not possible. Because wherever you go, there is light. Your own body actually gives off a minute level of visible light that you don't notice because it's so small or not in the right spectrum, as do other random objects. You literally glow.

But for the sake of argument, let's say you were in a completely light-free room. You aren't technically seeing darkness, but nothingness. And it just happens that nothingness looks a lot like darkness but they are not the same thing.

Your retinas aren't being activated because you aren't perceiving anything at all without photon data input. If you aren't seeing anything, that includes not seeing darkness. In fact, if you focus really hard in a completely dark room, what you will actually see is a gray called "eigengrau," which is a type of false light that your brain produces in the absence of light-sense data. Even blind people report seeing it. So in complete darkness, your brain will still produce a form of light for you to see.

There is also the problem of determining exactly where light ends and dark begins.

Darkness doesn't ever go anywhere because it never comes from anywhere. What we perceive as darkness is just the default state of our visual experience when we aren't seeing enough light. Light doesn't actually disperse darkness, it simply washes out our perception of it which is always mixed right in with the light we see. If we were to ever actually see absolute light without darkness, we'd go blind as it damaged our retinas.

If you're in a room with no light at all, you'd be the only source of light. You'd be the biggest source of light. But still, not very big in terms of visible light unless something can see you in the infrared spectrum. The amount of visible light we give off is about a thousand times less than what we typically pick up. But to certain animals, we probably glow a deep yellow in the dark.