I have no clue what Dark Matter is... but no, light is not the absence of darkness. The little story should have made that clear, but...

Darkness is not a "something" that can be negated or subtracted. It's an emptiness. An absence, a void. You can't negate a void because there really is no void in the first place to be negated. "Darkness" just appears as such due to how our senses perceive the lack of (or extremely low levels of) light (which is a "something"). Darkness, cold, space... are really the same underlying state of emptiness/nothingness, perceived differently due to the contrast of "things" placed against that "nothingness".

Darkness is the illusionary contrast created by the senses in the absence of light. Light is not an absence of darkness, or anything else. On the contrary, the existence of light causes our mind and senses to "create" the darkness in contrast to the light.

If you take complete emptiness, and add a light, the existence of that light creates the illusion of darkness beyond the boundaries of the light. So the emptiness is now perceived as darkness. Take the light away and add an object instead, and the contrast between the object and the emptiness creates the illusion of space out of the same emptiness that was previously perceived as darkness. Add a sound and suddenly you can become aware of silence as well.