Let's take a logical approach to this dilemma:Webster defines "dark" as "being without light, or without much light." To understand this we must know what light is. Webster defines light as "something that makes vision possible:EM radiation visible to the human eye." Given, there is a much more profound definition for light should you ask a Nebel Prize-winning physicist. However i am educated in matters of wave propagation and photon emittence, but i'm taking it back to the concrete streets here. So darkness is a state of being without something to make vision possible, or the absence of visible EM radiation. The use of the word "much" in the definition implies that there are different levels of this state that exist. It would follow that darkness is a natural state, and not an additive substance, matter, or entity (such as, well, light for example). So this gives the conclusion that darkness is not light in any way, but a combination of the two may exist simultaneously. And as such, a state of mixed ight and dark, or just dark, may indeed be observed by human vision, in the sense that "I can see that there is not light here, therefore it is dark." Or the reciprocal, "There is darkness here, that means there must be little of no light."